You might not feel decimals are the most exciting thing in the world, but just look at our friend 
, a decimal with its own holiday! In this edition of GMAT Math, we’re going over two specific types of decimals: terminating and repeating decimals. Learn about how to identify and solve questions with these decimals. Don’t forget to test your understanding with the practice questions at the end!
Rational Numbers
Integers are positive and negative whole numbers, including zero. Here are the integers:
{ … -3, -2, -1, 0, 1, 2, 3, …}
When we take a ratio of two integers, we get a rational number.
- A rational number is any number of the form a/b, where a & b are integers, and b ≠ 0.
- Rational numbers are the set of all fractions made with integer ingredients. Notice that all integers are included in the set of rational numbers, because, for example, 3/1 = 3.
Rational Numbers as Decimals
When we make a decimal out of a fraction, one of two things happens. It either terminates (comes to an end) or repeats (goes on forever in a pattern). Terminating rational numbers include:
1/2 = 0.5
1/8 = 0.125
3/20 = 0.15
9/160 = 0.05625
Repeating rational numbers include:
1/3 = 0.333333333333333333333333333333333333…
1/7 = 0.142857142857142857142857142857142857…
1/11 = 0.090909090909090909090909090909090909…
1/15 = 0.066666666666666666666666666666666666…
When Do Rational Numbers Terminate?
The GMAT won’t give you a complicated fraction like 9/160 and expect you to figure out what its decimal expression is. BUT, the GMAT could give you a fraction like 9/160 and ask whether it terminates or not. How do you know?
Well, first of all, any terminating decimal (like 0.0376) is, essentially, a fraction with a power of ten in the dominator; for example, 0.0376 = 376/10000 = 47/1250. Notice we simplified this fraction, by cancelling a factor of 8 in the numerator. Ten has factors of 2 and 5, so any power of ten will have powers of 2 and powers of 5, and some might be canceled by factors in the numerator , but no other factors will be introduced into the denominator. Thus, if the prime factorization of the denominator of a fraction has only factors of 2 and factors of 5, then it can be written as something over a power of ten, which means its decimal expression will terminate.
- If the prime factorization of the denominator of a fraction has only factors of 2 and factors of 5, the decimal expression terminates. If there is any prime factor in the denominator other than 2 or 5, then the decimal expression repeats.
Here’s some examples of this concept at work:
- 1/24 repeats (there’s a factor of 3)
- 1/25 terminates (just powers of 5)
- 1/28 repeats (there’s a factor of 7)
- 1/32 terminates (just powers of 2)
- 1/40 terminates (just powers of 2 and 5)
Notice, as long as the fraction is in lowest terms, the numerator doesn’t matter at all. Since 1/40 terminates, then 7/40, 13/40, or any other integer over 40 also terminates. Since 1/28 repeats, then 5/28 and 15/28 and 25/28 all repeat; notice, though that 7/28 doesn’t repeat, because of the cancellation: 7/28 = 1/4 = 0.25.
Shortcut Decimals to Know
There are certain decimals that are good to know as shortcuts, both for fraction-to-decimal conversions and for fraction-to-percent conversions. These are:
- 1/2 = 0.5
- 1/3 = 0.33333333333333333333333333…
- 2/3 = 0.66666666666666666666666666…
- 1/4 = 0.25
- 3/4 = 0.75
- 1/5 = 0.2 (and times 2, 3, and 4 for other easy decimals)
- 1/6 = 0.166666666666666666666666666….
- 5/6 = 0.833333333333333333333333333…
- 1/8 = 0.125
- 1/9 = 0.111111111111111111111111111… (and times other digits for other easy decimals)
- 1/11 = 0.09090909090909090909090909… (and times other digits for other easy decimals)
Irrational Numbers
There’s another category of decimals that don’t terminate (they go on forever) and they have no repeating pattern. These numbers, the non-terminating non-repeating decimals, are called the irrational numbers.
- It is impossible to write any irrational number as a ratio of two integers.
Mr. Pythagoras (c. 570 – c. 495 bce) was the first to prove a number irrational: he proved that the square-root of 
is irrational. We now know: all square-roots of integers that don’t come out evenly are irrational. Another famous irrational number is , or pi, the ratio of a circle’s circumference to its diameter. For example,
= 3.141592653589793238462643383279502884197169399375105820974944592307816
That’s the first 70 digits of pi, and the digits never repeat—they go on forever with no repeating pattern. There are infinitely many irrational numbers: in fact, the infinity of irrational numbers is infinitely bigger than the infinity of the rational numbers, but that gets into some math that is much more advanced than what you need to know for the GMAT.
Terminating and Repeating Decimals: Practice Questions
Now here’s your chance to test your understanding! Try to answer these practice questions and then check the answer and explanation.
- 2/27
- 3/2
- 3/4
- 3/8
- 9/16
Show answer and explanation
From our shortcuts, we know 0.166666666666… = 1/6, and 0.444444444444… = 4/9. Therefore (1/6)*(9/4) = 3/8.
Answer = D
And now for a sample question from our GMAT product:
2. Given that
represents a decimal in which the digit k repeats without end, then what is the value of 
?0.1
1
4.5
6
18
Click here for the answer and video explanation!
If you’d like to practice more with decimals, check out our GMAT practice questions with fractions and decimals.
I have a question, 100/3=33.333…. and the division keeps on going , this means if we multiple 33.3333….with 3 result should be exactly equal to 100 but we get 99.99999…..why?? And only the calculators show 100 but practically doing we get 99.99999…..Please explain
Hi Sam! Great question. The answer here is simple but frustrating. We get 99.9999… instead of 100 because calculators are imperfect! Most calculators are simply not good at properly calculating multiplication with infinitely repeating decimals. You are correct that 33.33333…(repeating) should be 100 when it’s multiplied by 3. And on a sufficiently sophisticated calculator, it would be. However, most calculators are not properly programmed to do this operation correctly.
The good news is that you can still do this calculation correctly on any calculator that can multiply fractions. Simply convert 33.33333… to 33 and 1/3, or 100/3. From there, multiply 100/3 by 3, and you’ll get the 100 you’re looking for. This works anytime you can convert an infinitely repeating decimal to a fraction. 🙂
is 2/5 and – 2/3 a repeating or terminating decimal
Hi Jason,
2/5 is a terminating decimal, and -2/3 is a repeating one. 🙂
What is 2/9, 3/9, 4/9, 5/9, 6/9, 7/9, 8/9 as a decimal please tell me is it is terminating or not terminating. THANKS!!!
Hi Ellie!
1/9 = 0.11111111111… and it is a repeating decimal.
Therefore,
2/9 = 0.22222222222…
3/9 = 1/3 = 0.3333333…
And so on and so forth. 🙂 These are all non-terminating, repeating decimals.
To get the rest, you just multiply 0.11111… by your number of interest. 😀
Is 5/11 in a repeating or terminating decimal
Hi Amanda,
It is a repeating decimal, because we have 0.454545… that never ends. Hope that helps!
Is 2/5 a repeating or termanting decimal?
It is terminating!
I think this website is useful
Is there any decimal expansion of rational number that repeated and terminate?
If I understand the question correctly, you’re wondering if there are any rational numbers where the decimal repeats, but repeats for a finite amount of time, and then terminates.
There definitely are. For example, the number 1.2525 is the same as the ratio 12,525/10,000 (or 501/400, in simplest terms). The “25” repeats twice and then terminates, and this is completely expressable as a fraction or ratio. There are plenty of other examples too, since any number that repeats for a time and then terminates will be rational.
Hi,
When dividing to get a decimal and adding zero to the dividend to continue the quotient, how do you know when to stop? I always thought that once you see a number repeat three times with the same subtraction pattern that it was enough to show that it repeats. However, I noticed that pi has some digits that repeat up to nine times! Does this only happen with irrational numbers and what’s the max number of digits that will repeat? Thanks!
That’s a really good question, Angie. 🙂 In a strict mathematical sense, you could have a rational number that has a pattern of hundreds or thousands of digits that repeat. Or more. There really is no limit. However, in a GMAT mathematical sense, you only need to worry about repeating decimals for simple ratios such as 1/3, 1/7, 1/9, etc…. The longest strong of repeating decimals you’ll lkely have to deal with on the exam is 1/7 specifically. There you have a pattern of 6 decimals that repeats. You may have to deal with 1/13 (8 repeating decimals), but it won’t get more complex than that on the test.
If you’re curious, this web page indexes several PDFs that list the number of digits in a repeating pattern for a very large set of fractions. Type “ctrl-f” and enter the phrase “repeating digits” into the search to find the PDFs in question.
Can you help me is 4.65 eight terminate number or a repeated number And same with 0.68
Hi Brit,
Any number that ends is a terminating number. So 0.5 or 0.1276 or 0.11736 (and infinitely many others) are terminating. In contrast, repeating decimals are those that go forever. So 1/3 is 0.333… repeating infinitely. Or 1.851851851… if it does not end, it is a repeating decimal. 🙂
hey can u please help me with a question
whether pie{22/7} is a rational number or not?
Hello! Pi is an irrational number. 🙂
Thank you this really helped me a lot in math thanks Mike. 🙂 😛
you told me what my math teacher did (but I actually got it this time).
Thanks/Cheers
hello,
what are two examples of rational numbers, one taht can be wrtitten as a terminating decimal, and one that terminates?
tank you
happy to help. But I think you meant you wanted two examples of rational numbers, one that can be written as a REPEATING decimal and one that terminates. (“One that can be written as a terminating decimal” and “one that terminates” mean the same thing, of course!)
In this article, under the heading Rational Numbers as Decimals, Mike gives several examples of rational numbers as repeating decimals, and several examples of rational numbers that terminate. Then, under the heading When Do Rational Numbers Terminate, Mike explains that rational numbers terminate if their denominators contain only factors of 2 or 5 (or factors of both 2 and 5). Otherwise, rational numbers will repeat.
Based on that rule, here are two additional examples each for rational numbers that repeat and terminate.
Repeating rational numbers: 1/66, 3/19 (Denominator 66 has a factor of 2, but also factors of 11 and 3; denominator 19 contains neither factors of 2 nor of 5.)
Terminating rational numbers: 26/25, 51/200 (Denominator 25 contains only factors of 5; denominator 200 contains only factors of 5 and 10.)
Is 64\455 is a terminating decimal
Hi Shyam,
Nope, it is a repeating decimal. Check it out on Wolfram Alpha.
is 1/99 terminating?
Hi Sam,
1/99 is a repeating decimal.
1/99 = 0.0101010101….
Would thirty-three over forty be considered a terminating or repeating decimal? Thank you, love the site.
Hi Luciann,
33/40 is equal to 0.825 and as we have a finished expression that does not continue indefinitely, it is a terminating decimal. 🙂
is 7/10 a terminating decimal or an equivalent fraction
Hi Sam,
“7/10” is a terminating decimal. It can also be an equivalent fraction. For example, “7/10” and “14/20” are equivalent fractions.
Is a whole number considered being a terminating decimal? e.g: 1400
Hi Bob,
Yes, whole numbers are technically considered terminating decimals as the digits do not go on forever.
7/15=.46 with bar notation
so is this terminating, non-terminating, repeating, or non repeating
3/5=.60
so is this terminating, non-terminating, repeating, or non repeating
9/16=.5625
so is this terminating, non-terminating, repeating, or non repeating
1/3=.33 with bar notation
so is this terminating, non-terminating, repeating, or non repeating
7/15 and 1/3 equal repeating decimals. 3/5 and 9/16 are terminating decimals.
What is 9/20 in a terminating decimal form?
Hi Jessica,
9/20 creates a terminating decimal that is equal to .45 🙂
Hi can help me for this problems 10/12 7/72 15/75 9/14 35/40
10/12 actually creates a repeating decimal, 0.83 with 3 repeating. 7/72 is also a repeating decimal, 0.972 with 2 repeating. 15/75 is the non-repeating 0.2, or 1/5 (1/5 being what 15/75 simplifies to in fraction form).
9/14 is tricky. It amounts to a fairly complex repeating decimal: 0.642857142857… with 142857 repeating. (This is because 142857 is a repeating number in fractions that involve dividing by 7 or dividing by certain multiples of 7. See this for more info: https://www.douglastwitchell.com/142857calculator.php )
35/40 is the same as 7/8, which is the non-repeating decimal of 0.875 .
is 5/12 a repeating or terminating decimal
is 7/8 a repeating or termination decimal
Hi Jada,
5/12 is 0.41666… repeating, so it is a repeating decimal.
7/8 is 0.875 and it ends, so it is a terminating decimal.
Hope that helps! 🙂
What does 1/11 turn into as a decimal?
1/11 becomes 0.090909… repeating the 09 forever!
What is repeating fraction for two fiftieths, eleven twentieths
Hi Laura,
These values are not repeating decimals. Check it out:
2/50 = 4/100 = 0.4
11/20 = 55/100 = 0.55
I hope that helps! 🙂
I helped me out thanks???
Why is it than when 1.4999999999… is converted to a fraction it is equal to 3/2 which would be the fraction of a different decimal as well (1.5)? What would be the explanation to this?
Hi Kaylee,
This can be hard to wrap your mind around. There is a similar and commonly-discussed argument that 0.999…. is equal to 1. This is an example of a discussion on that topic: https://www.math.hmc.edu/funfacts/ffiles/10012.5.shtml. The explanation can be extremely complicated depending on the mathematical level of the person trying to prove the point, so be careful not to fall too deeply down a math rabbit hole! 🙂
Wait…
22/7 and 3.1415… (π) are the same, but when you pry in closer they aren’t.
To prove my point, 22/7 = 3.142857…
Meanwhile, π is 3.14159265358979…
How are they equivalent?
Or are they just said to be equivalent
Hi Daniel,
You’re right! 22/7 is an approximation of pi, and a pretty famously used one at that. It’s not the real thing because pi cannot be expressed as a ratio of integers, but it’s near enough for many purposes. This is because pi is irrational and so we have to make an approximation in order to be able to do any kind of easy notation. There are other approximations like that such as 333/106, and 355/113. Hope that helps. 🙂
Hi, thank you always for the wonderful articles.
I have a question, if
0.111… = 1/9
0.888… = 8/9
is 0.999…= 9/9? (Well, no, right?)
How does that logic work again?
Hi Jane,
Happy to help! 🙂
In mathematics, the repeating decimal 0.999… denotes a real number that can be shown to be the number one. In other words, the symbols “0.999…” and “1” represent the same number. There are tons of mathematical proofs that work through this (at varying levels of difficulty), but this page gives a brief explanation. You can also read about this on Wikipedia! I hope this helps get you started. 🙂
Is -54/19 irrational. When do you end or terminate a decimal,up to what place?
Thanks
Hi Vee,
Good question! Wolfram Alpha is amazing for things like this. You can see here that -54/19 is actually rational, but it has a repeating period of 18 digits. There is no standard place to terminate a decimal–in this example, the decimal needs to go 18 places to see the full extent of its period!
Hi is it possible to be terminating decimal even if denominators cannot be expressed as powers of 2 and 5 for ex-
is 39/128 a terminating decimal?
Hi Gayathri,
Happy to help! As mentioned in the post, “If the prime factorization of the denominator of a fraction has only factors of 2 and factors of 5, the decimal expression terminates. If there is any prime factor in the denominator other than 2 or 5, then the decimal expression repeats.” So, no, a denominator whose prime factorization includes other primes besides 2 and 5 will not terminate.
In terms of your question, 128 = 2^7 and thus can be expressed as a power of 2. Furthermore,
39/128 = 0.3045875
Because the decimal ends at some point, it is a terminating decimal. In this case, if we were to multiply the fraction by 10^7, we would see that the quotient would be an integer:
39/128 * 10^7 = 390,000,000/128 = 3,046,875
On the other hand, it is not possible to do this with repeating or irrational numbers to get an integer quotient.
Hope this helps! 🙂
hi
which one is a terminating decimal?
1/3
7/9
2/5 or
5/6
Hi Sabrina,
Terminating decimals are decimals that eventually come to an end, while repeating decimals go on forever. In terms of the fractions you asked about:
1/3 = 0.3333… (where the 3 repeats)
7/9 = 0.7777… (where the 7 repeats)
2/5 = 0.4 (this decimal ends, so it is a terminating decimal)
5/6 = 0.8333… (where the 3 repeats)
As you can see, the only example above of a terminating decimal is 2/5 = 0.4
Hope this helps!
is 7/18 a terminating decimal?
Hi Kaitlynn,
No, 7/18 is not a terminating decimal. As a decimal
7/18 = 0.3888… (where the 8 repeats)
Hope this helps 🙂
Does the line mean it terminates or repeats
Hi Frankie,
A line over one or more digits in the decimal place indicates that the digit (or digits) repeat(s) 🙂
Hope this clears things up for you!
Can a number be rational in fraction form (22/7) and irrational in decimal form (3.141592653. . .)? As a middle school math teacher, we say any number that can be expressed as a fraction is rational, yet some fractions are not repeating or terminating in their decimal form. What’s the mathematician’s answer to this?
Hi Kim,
Yes! There are many examples of this! A classic one is pi, as you pointed out. In order to calculate pi, you divide the circumference of a circle by it’s diameter. Both the circumference and diameter are numbers that form a fraction (22/7) but when you divide 22/7 you get an irrational number, pi. In fact, there is no rule saying that a rational fraction must be rational in decimal form. This is why it is sometimes convenient to represent irrational numbers in their decimal form for a more precise answer.
Hello,
I think 22/7 in decimal is still rational since you can see a repeated pattern with the numbers.
Hi Emerzen,
You’re right. 22/7 is an approximation of pi. It’s not the real thing because pi cannot be expressed as a ratio of integers, but it’s near enough for many purposes. This is because pi is irrational and so we have to make an approximation in order to be able to do any kind of easy notation. There are other approximation like that such as 333/106, and 355/113. Hope that helps. 🙂
in the decimal 0.15.why is there a line over the number 15
Hi Debra,
Happy to help! 🙂 The line means that the numbers occurring under the line repeat infinitely. I hope that clarifies!
is 1.765 a rational or irrational number and where would it fall o a number line????
Hi Ta’jhai!
In mathematics, an irrational number is a real number that cannot be expressed as a ratio of integers, i.e. as a fraction. Therefore, irrational numbers, when written as decimal numbers, do not terminate, nor do they repeat. A good example of an irrational number is pi.
The decimal 1.765 that you mention can be written as many fractions, including 353/200. Therefore, it is a rational number. It would fall between 1 and 2 on a number line of only whole numbers. It would be possible to give an infinite number of places it would fall depending on the specificity of your number line units. For example, it could also be between 1.764 and 1.766 if you had decimals that specific.
I hope this helps! 🙂
How do you decide by which power
of 10 to multiply an equation when writing a
decimal with repeating digits as a fraction?
Hi Emma 🙂
Usually, we use this method only for terminating decimals. To determine which power of ten to use, you need to count the number of decimal places from the decimal point to the end of the terminating number. That will give you the power of 10 by which to multiply. For example, let’s say we have the decimal
0.004137
To see what power of 10 we should multiply by to write this decimal as a fraction, we start at the decimal point and count the places until reaching the final digit, 7. There are 6 digits, so we will multiply this decimal by 10^6:
0.004137*10^6 = 4137
And to write the decimal as a fraction, we need to divide this integer 4137 by 10^6:
0.004137 = 4137/1,000,000
For repeating decimals, there’s no power of 10 by which we can multiply to be able to rewrite the decimal as a fraction. Rather, dealing with repeating rational numbers is a matter of recognizing familiar patterns and guess and check to determine the equivalent fraction.
I hope this helps, at least a little 🙂
Can I know where will I put the terminating and repeating decimals if I make a map about Real Numbers ?
If I understand correctly, you’re asking where repeating decimals would fit in a concept map of real numbers, such as this one: http://edtech2.boisestate.edu/dougwolfe/images/real_numbers2.jpg . In any concept map of different categories of real numbers, numbers with repeating decimals would fall under the category of rational numbers— numbers that can be expressed in fraction form. All repeating decimal numbers have a fraction expression. 1/3 is 0.333333333 repeating, 2/7 is 0.285714 repeating, and so on. Rational numbers also includes terminating decimals, such as 2.25 (9/4 in fraction form).
can you help me
why 0 is included in even numbers
Hi Mohammad,
This is just a quirk of how numbers are classified. While 0 is neither negative nor positive, it is considered an even number. 🙂
sir,
how to convert 0.07 into fraction and 7 is repeating decimal…
please sir help me
Hi there 🙂
Happy to help! Firstly, let’s look at 0.07 or seven hundredths. As its name suggest, seven hundredths is 7 parts of 100. So, we can rewrite 0.07 as
0.07 = 7/100.
In terms of 0.777…, here’s a nice trick. For repeating decimals that have the same repeating digit, from 0.111.. to 0.888…, as fractions, they are that digit over 9:
0.111… = 1/9
0.888… = 8/9
etc.
So, 0.777… repeating is equivalent to 7/9.
Hope this helps! 🙂
Hey can u help me what’s the decimal expansion of the rational number 1/9 repeats.
Hi Autumn,
1/9 = 0.111… where 1 repeats indefinitely in the decimal part of the number.
sir,
please help me in mine situation as my exams are nearer.
which least number must be divided
to 2/5×7 to make it terminating decimal expansion
plz sir reply me fast
I m waiting for your reply
Hi Tanu 🙂
Let’s look at the two factors in the denominator:
5: 1/5 = 0.2 and is therefore a terminating decimal
7: 1/7 = 0.142857… The decimal does not terminate but rather repeats as 1428567.
So, if we want to create a terminating decimal from 2/(5*7), we must multiply by 7. By multiplying by 7, we can cancel the term of 7 in the denominator, leaving us with a factor of 5, which will give us a terminating decimal:
2/(5*7)*7 = 2/5 = 0.4
I hope that helps!
Pi is an irrational number. Pi is ratio of circumference to its diameter. But if we make a circle with rational diameter say x then we will get a circle with circumference of rational value i guess. Now if we take the ratio it should be rational. Then why pi is irrational
Hi Rohan 🙂
Pi is an irrational number because when written as a decimal number it does not terminate or repeat. The circumference of a circle, C, is defined as 2(pi)r, where r is the radius of the circle. Since 2r = d, then C = d(pi) and C/d = pi. With that in mind, you’ll find that we cannot write pi as a ratio of two rational numbers. Typically in GMAT questions, you’ll be given either the radius or diameter as a rational number. That means that the circumference will be pi multiplied by that rational number. Since pi is irrational, the circumference in that case will also be an irrational number.
That said, physically measuring the exact circumference of a circle with a rational radius is not possible and requires estimation, which can result in a very good approximation of the circumference. The precision of that approximation can be tested by comparing the experimental C/r ratio with pi.
And if you’re interested, you can read up about the proof that pi is an irrational number on Wikipedia.
Hope this helps 🙂
hey can u please help me with a question
whether pie{22/7} is a rational number or not?
Hi Samridhi,
Good question! 🙂 The popular approximation of 22/7 = 3.1428571428571… is close but not quite accurate for pi. In either case, pi is a famous irrational number! I hope that helps. 🙂
Why do calculators put a 7 as last decimal digit when dividing numbers like 2, 5, 20, 40, 80, 110, 140 and so on by 3? Calculating by hand the result has a never ending 6 as decimal. How do they get the 7?
Hi Zsombi,
Good question! 🙂
The calculator is forced to round up by the end of its display, and a repeating 6 decimal would warrant rounding up to 7. But you are right, it is actually a never-ending 6. I hope that makes sense!
Hii
Can u plz help me
I have a question
Is root 6 + root 9
Rational??
Hi Gauri,
Happy to help! The sum of a irrational number and rational number is irrational. In this case, we have
sqrt(6) + sqrt(9) = sqrt(6) + 3
Sqrt(6) is an irrational number and is 2.4494… w
So, the sum is
2.4494… + 3 = 5.4494…
The three dots represent the irrational decimal part of sqrt(6). Since the decimal does not terminate, the decimal in the sum will not terminate either. Therefore sqrt(6) + sqrt(9) results in a irrational number.
Hope this helps 🙂
What if the number is 3.067 but only the 7 has a repeating line over the number. Is that rational or irrational?
Hi Jason,
A number can be a rational number and not have the first decimal place repeating. Consider some common repeating decimals:
1/6 = 0.1666…
5/6 = 0.8333…
1/12 = 0.08333…
5/12 = 0.41666…
I do not know off hand what the fraction representation of your suggested 3.0677… would be, but presumably we could find a ratio of two integers that would create that number, making it a rational number. 🙂
No. On a number line 1 is farther away from 0 than .75
Would .75 be bigger than 1?
No it would be smaller because 1 is a whole number and .75 is 3/4 of a whole so 1 is bigger
Thanks
Great article Mike!!!
Dear Hamza,
I’m glad you found this helpful! Best of luck to you!
Mike 🙂
Hi Mike definitely great explanation about rationals and irrationals.
I have a question.
Is there some sort of formula to determine when a decimal number is Irrational? so it can be implemented by code.
Thank you.
Matt Hall,
Matt,
I’m happy to respond. 🙂 Everything about the relationship of rationals and irrationals defies all attempts to encapsulate it in a formula. For simple GMAT purposes, the GMAT will give you a decimal with, say, 10 or 12 places after the decimal showing. Either there will be a simple repeating pattern or not. If there’s a repeating pattern, the number is rational. For GMAT purposes, if the decimals shown contain no repeating pattern, then we can assume the decimal is irrational. Technically, the GMAT never asks about rational or irrational anyway: that’s already between the GMAT.
Now, in the bigger picture, it’s certainly true that there are decimals that have repeating patterns that consist, say, of a string of some large number of decimals. For example, the decimal pattern of 1/29 repeats a pattern that is 28-decimal-places long:
1/29 =
0.03448275862068965517241379310344827586206896551724137931
03448275862068965517241379310344827586206896551724137931
03448275862068965517241379310344827586206896551724137931 . . .
(courtesy of Wolfram Alpha)
As I am sure you appreciate, if you have only, say, the first 12 decimals places, there are an infinity of possible rational numbers and another, larger infinity of possible irrational numbers that start with those initial 12 decimals. Having 12 decimal places, while extremely precise, is known mathematically as a decimal approximation, a sharply curtailed approximation of the infinite decimal. From a mathematical point of view, if we have 12 decimal places, we have essentially nothing. Mathematician regularly examine decimals to millions and billions of decimal places. For example, in 2014, pi was calculated to 13,300,000,000,000 decimals. If we are looking at any number that can be printed on a single sheet of paper, on a single line of text, then, from a purely mathematical point of view, that’s kiddie pool stuff.
Basically, there’s no code as efficient as the human mind on this. However many decimals we have, the question is simple: do we see a repeating pattern or not? The human brain is a better pattern-detecting and pattern-matching machine than any computer.
Does all this answer your question?
Mike 🙂
Example of 9/160 at top of the page is wrong. You forgot to add 0 after decimal point.
Dear “John”,
Very perceptive! Thank you very much for pointing out that typo. I just corrected it. Best of luck to you, my friend.
Mike 🙂
Can you please give an example of the division problem of 1/8 converted into a decimal and can you tell me if the answer is terminating or if it’s repeating?
If a denominator have prime factors of only 2 or only or both then the number terminates ( because any denominator will be in the form ten’s , so factors of 10 is 2* 5 )
If the denominator factors are other than 2 and 5 then the decimal repeats
But taking an ex 1/14 ( factors are 2 and 7 ) it has a repeating decimal.
It’s very useful,thank you.Is my understanding is Right?
Dear Anusha,
Your understanding is correct. For example, 1/35 has 5 & 7 in the denominator, so this would be a repeating non-terminating decimals.
1/35 = 0.0285714285714285714 …
But, notice, if we put something divisible by 7 in the numerator, then the sevens would cancel, and the fraction would terminate:
21/35 = 3/5 = 0.6
Does all this make sense?
Mike 🙂
If the number is itself 2 & 5. And if multiplies it with 5/2 and gives answers in which digit in ones place is 0 then that number will terminates always for example
3/4 it will terminates
4*5/2=10 ad we got 0 at ones digit we can easily identify it.
Dear “anonmoyous” or “anonymous”,
Yes, I believe if I understand you correctly, we are saying very much the same thing. You seem to understand this issue well, which is great. Best of luck to you.
Mike 🙂
Give me some reasons why 1/6 is irrational number?
Hi Fariha,
Happy to help! 🙂 Can you tell me why you think 1/6 is an irrational number? 1/6 is actually not an irrational number because we can express it as a ratio of integers or a fraction! I hope that helps. 🙂
Hi Mike…
Thanks a ton for this explanation..I just gave a Practice Test from GMAC ( the new Exam pack) and got two questions to do with terminating decimals…Have my GMAT in 36 hours from now..I have absolutely loved the Magoosh product…Hope to get a good score on Monday and write a good testimonial for Magoosh 🙂
Dear Nishant,
You are quite welcome. I am very glad you found this blog article helpful, and I’m glad you like the Magoosh product. Best of luck to you my friend!
Mike 🙂
Found what i was looking for!
Thanks this really helped! 🙂
Dear Saketh,
I’m glad it helped you. Best of luck to you!
Mike 🙂
I didn’t find what I was looking for, but it is very useful! 🙂
Thank You for spreading your knowledge with others.
Sincerely,
Sara
Well, thank you. I hope you find that for which you seek. Best of luck to you.
Mike 🙂