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Chris Lele

SAT Math – Number Basics

What you need to know for the SAT from a basic level? Well, below is a pretty good answer. Though the information below won’t pertain to every question, they are important fundamentals/terminology that you should know walking into the test.


Prime numbers

A prime number is a number divisible by itself AND 1.

1 is not a prime number because 1 IS itself. Don’t worry if your head can’t wrap around that logic. Just remember, 1 is not a prime number.

2 is the lowest prime number and the only even prime. It is good to be familiar with the prime numbers up to 30, though you don’t have to memorize them.


Multiples, divisors, and factors

A multiple of n results if you multiply n by any positive integer. For instance,

3 x 1 = 3,

3 x 2 = 6,

3 x 3 = 9

3 x 4 = 12

These are all multiples of 3.

A factor is a smaller part of a larger number. Mathematically, factors are the numbers that form a larger number when you multiply them. In the example using 24 below, ‘2’ and ‘12’ are factors of ‘24’ because when you multiply them together you get 24.

24: 1, 2, 3, 4, 6, 8, 12, and 24 are factors of 24 (note that ‘24’ is both a factor and a multiple of ‘24’. In math terms, for every integer n, n is both a factor and a multiple of itself.

The prime factors of a number are the factors broken down to prime numbers. To find the prime factors, choose two factors of a number, say ‘3’ and ‘8’ (3 x 8 =24). Keep figuring out the factors for the number(s) that remain that are not primes. ‘3’ is a prime; however, ‘8’ is not. It can be broken into 2 x 2 x 2. Therefore, the prime factors of ‘24’ are 2, 2, 2, and 3.


Evens and odds

Odd + odd = even

Odd + even = odd

Even + even = even

Don’t feel you have to memorize these. You can just plug in any odd or even number to derive the relationships.


Percent fraction decimal conversion

1% = 1/100 = .01

10% = 1/10 = .10

50% = ½ = .5


Adding fractions and multiplying factions

A quick trick for adding two fractions in which the numerator for both is ‘1’:

The numerator equals the sum of the numbers in the denominator; the denominator is the product of these two numbers. In the fraction below, all I have to do is add 2 and 3 for the top (giving me 5) an multiply 2 x 3 for the bottom (giving me 6).

½ + 1/3 = 5/6

Some other examples:

¼ + 1/6 = 10/24 = 5/12

1/5 + 1/7 = 12/35

1/3 + ¼ = 7/12

For multiplying fractions, just multiply across the numerator and across the denominator.

2/3 x 4/5 = 6/15 = 2/5

3/10 x 5/2 = 15/20 = ¾

½ x ¼ x ½ = 1/16


About Chris Lele

Chris Lele is the GRE and SAT Curriculum Manager (and vocabulary wizard) at Magoosh Online Test Prep. In his time at Magoosh, he has inspired countless students across the globe, turning what is otherwise a daunting experience into an opportunity for learning, growth, and fun. Some of his students have even gone on to get near perfect scores. Chris is also very popular on the internet. His GRE channel on YouTube has over 8 million views.

You can read Chris's awesome blog posts on the Magoosh GRE blog and High School blog!

You can follow him on Twitter and Facebook!

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