For a start, give these problems a try. A complete explanation will come at the end of the discussion.

1) When positive integer N is divided by positive integer J, the remainder is 14. If N/J = 134.08, what is value of J?

- 22
- 56
- 78
- 112
- 175

2) When positive integer N is divided by positive integer P, the quotient is 18, with a remainder of 7. When N is divided by (P + 2), the quotient is 15 and the remainder is 1. What is the value of N?

- 151
- 331
- 511
- 691
- 871

3) P and Q are both positive integers. When P is divided by Q, the remainder is some positive integer D, and when P is divided by (Q + 3), the remainder is also D. If P/Q = 1020.75 and P/(Q + 3) = 816.6, then which of the following gives the correct set of {D, Q}?

- {6, 12}
- {6, 15}
- {9, 12}
- {9, 15}
- {15, 24}

I will discuss those questions at the end of this article.

## Division Terminology

Let’s look at division carefully and think about the parts. Suppose we divide 33 by 4. Of course, 4 goes into 33 eight times, with a remainder of 1. Let’s talk about the official names of this cast of characters.

33 = the **dividend** = the number being divided

4 = **the divisor** = the number doing the dividing; the number by which you divide

8 = the integer **quotient** = the integer that results from a whole number of divisions

1 = the **remainder**

We have to add a caveat here. Notice: here we are talking about positive integers only —- living in the magical fairyland where the only numbers that exist are positive integers, where skies are not cloudy all day. Unless you live on a farm where the barnyard animals all sing in unison, you don’t get to stay here forever.

Of course, numbers in the real world aren’t like that, and if you prance through the GMAT Quantitative Section as if it’s a magical fairyland where all the numbers are positive integers, this section will utterly decimate you. In the real world that involves all possible numbers, this process looks a bit different. For example, if you type 33/4 into your calculator, your calculator will tell you

33/4 = 8.25

That decimal, 8.25, is the quotient, the actual real-world mathematical quotient. In this article, for clarity, I will refer to this one as the “decimal quotient.”

Notice, first of all — the integer part of the decimal quotient is exactly equal to the integer quotient. It has to be. In fact, we can go a little further: Let’s look at this process both with words and with numbers:

We divide the dividend (33) by the divisor (4), and we get the decimal quotient. The integer part of the decimal question is the first piece of the last sum, the integer quotient. What’s crucially important is — the decimal part of the decimal quotient equals the final fraction:

Virtually any problem on the GMAT that gives you a decimal quotient is relying on this particular formula. It is crucial for answering #1 and #3 above.

## Rebuilding the Dividend

Let’s go back to the integer relationships:

If you are given the divisor, the integer quotient, and the remainder, then you can rebuild the dividend. In particular, notice that “divisor” is the denominator of both fractions, so we if multiple all three terms by “divisor”, it cancels in two of the three terms:

dividend = (integer quotient)*(divisor) + remainder

That formula is pure gold in questions which give you an integer quotient, a divisor, and a remainder. Even if one or two of those three are in variable form, it allows us to set up an algebraic relationship we can solve. This is crucial for answering #2 above.

## Practice Questions

It may be, at this point, you want to give those three questions another attempt before reading the solutions. Here’s yet another practice question:

4) http://gmat.magoosh.com/questions/305

## Practice Question Solutions

1) We know that

So 0.08, the decimal part of the decimal quotient, must equal the remainder, 14, divided by the divisor J.

0.08 = 14/J

0.08*J = 14

J = 14/0.08 = 1400/8 = 700/4 = 350/2 = 175

So J = 175, answer = **E.**

2) Use the rule **dividend = (integer quotient)*(divisor) + remainder** to translate each sentence.

The first sentence becomes N = 18P + 7. The second equation becomes N = (P + 2)*15 + 1, which simplifies to N = 15P + 31. These are ordinary simultaneous equations (http://magoosh.com/gmat/2012/gmat-quant-how-to-solve-two-equations-with-two-variables/). Since they both equal N already, let’s set them equal and solve for P.

18P + 7 = 15P + 31

3P + 7 = 31

3P = 24

P = 8

Now that we know P = 8, we can just plug in. The product 15*8 is particularly easy to do, without a calculator, by using the “doubling and halving” trick. Double 15 to get 30, and take half of 8 to get 4 —- 15*8 = 30*4 = 120. So

N = 15(8) + 31 = 120 + 31 = 151

N = 151, answer = **A.**

3) Here, we have to use

to translate each act of division. The first one tells us 0.75 = D/Q, and the second one tells us that 0.60 = D/(Q + 3). These are also two simultaneous equations. Multiply both to get rid of the fractions.

D = 0.75*Q

D = 0.60*(Q + 3) = 0.60*Q + 1.80

Both are equal to D, so set them equal to each other and solve for Q.

0.75*Q = 0.60*Q + 1.80

0.15*Q = 1.80

Q = 1.80/0.15 = 180/15 = 60/5 = 12

Now that we know Q = 12, we can find D = 0.75*Q = (3/4)*12 = 9. So D = 9 and Q = 12. Answer = **C**.

Thanks Mike- you’re phenomenal as always. This is a great lesson

But I’m intrigued– why have we not seen this rule before

Meaning, decimal part = remainder/divisor… i haven’t seen it anywhere

Dear Aisha,

Thank you for your kind words. I’m very glad you have found this helpful. Yes, it’s funny: not many people talk about this math factoid. It doesn’t often show up on the GMAT, and when it does, it is usually on the harder math questions. It’s peculiar that no one else mentions it, because it could be important on a question.

Mike

Dear Mike,

Thanks for all your great methods and suggestions. It was of great help to me and it made me nail my Gmat. Thanks!

Niels,

Congratulations! You are more than welcome! Best of luck in your future!

Mike

I am confused about a part of the explanation given for problem three. If the decimal part of the decimal quotient is remainder/divisor, then why is 0.75 D/Q and not R(remainder)/D ?

Nadeen,

That problem is a little confusing because it uses different letters. Notice, in that problem D is the remainder and Q is the divisor. Don’t be fooled by letters alone — you always have to look at the concepts behind the letters.

Mike

very nice, very helpful

Sadie,

Thank you for the kind words. Best of luck to you.

Mike

Dear Mike, Thanks for yet another terrific blog post!

BTW, how does this shortcut to solve Q # 3 look?

Since, it is given P/Q = 1020.75 and remainder is D, D/Q= 0.75 which is 3:4. The only answer choice that satisfies this condition is ‘C’

Thanks!

Dear Mensa Member,

Yes, that’s a great shortcut. Of course, if this had been a true GMAT-style question, probably there would have been more than one choice for which that ratio was true. I didn’t think to include that when I wrote the question, but that’s precisely the kind of thing they would see.

Does this make sense?

Mike

Yes, that would be a deadly GMAT trap, if one was not careful. Thanks, Mike, for the insight!

You are more than welcome.

Best of luck to you.

Mike

That’s what I did as well, and I would have chosen “C” on the GMAT, but I doubted because it seems to completely disregard the second remainder/divisor which is 60/100 or 3/5. How does that come into play?

Dear Katie,

I’m happy to respond. Remember, in that second division, the divisor is (Q + 3). We would have to add three to the second number in each answer pair, and then check the ratios — for {9/12}, the division we would check is 9/(12 + 3) = 9/15 = 3/5.

Does this make sense?

Mike

Hi Mike,

I did not understand the below part. In words, it says divisor/dividend but in numbers dividend/divisor which is actually correct. Could you please elaborate more on this as in connection between word and number formula below?

{divisor/dividend} = decimal quotient = interger quotient + {divisor/dividend}

{33/4}= 8.25 = 8 + {1/4}

Dear Sarika,

I’m sorry. There were a couple typos in that line, I believe I have corrected everything. Thank you for pointing this out, and let me know if there is anything that still doesn’t make sense.

Mike

Thank you. I studied four semesters of math while in college (25= years ago) and never learned this. Frightening. But wow will this help with problems like this on the test.

Jeff — it’s funny — I think most of us heard about this when we were in late grade school, but at that point, mathematical niceties were lost on us, and then going through puberty blurred everything. Unfortunately, many math teacher do not return to these basic subjects when students are older and able to understand the underlying logic. For example, it helps to think about this topic with algebraic symbolism, but when we first learned it in the fourth grade, we hadn’t learned algebra yet! I’m glad you found this helpful. Thank you for your kind words.

Mike

Thanks! Thanks to you I finally got a good method for remainders problem.

You are quite welcome.

Mike

Very nice set of material here. Thanks for the information.

Thank you for your kind words. Best of luck to you.

Mike