sat math

Factors

a factor is any whole number that divides neatly into another whole number

Multiples

A multiple is any whole number multiplied by any other whole number.

Prime numbers

a prime number ny number that has exactly two factors: itself and 1.

All prime numbers are positive, and all are odd except for 2, which is the only even prime number.

Zero and 1 aren’t prime numbers.

Composite numbers

any whole number with more than two factors (in other words, not

prime) is composite. If you can divide a number by a smaller whole number (other than 1)

without getting a remainder, it’s a composite number. Note that any composite number can be

divided down to its primes.

digits add to a multpile of 3

Any number whose digits add up to a multiple of 3 is also divisible by 3. 

ex, the digits of 789 add up to 24 7 8 9 24 ; because 24 is divisible by 3, so is 789.

digits add to a multiple of 9

 If the digits of a number add up to a multiple of 9, you can

divide the number itself by 9. 

ex, the digits of 729 add up to 18 7 2 9 18 ; because 18 is divisible by 9, so is 729.

numbers ending in 0…

Any number ending in 0 or 5 is divisible by 5.

numbers ending in 5…

Any number ending in 0 is divisible by 10.

real vs. imagionary numbers

real: any number found on a number line

imagionary: the square root of –1, also known as i.

undefined numbers

An undefined number doesn’t have a meaning.

The most common undefined number, and the only one that you have to consider for the SAT, is a number divided by zero. You don’t actually work with this, but if the question shows 2/3-x , then somewhere in there, it’s guaranteed to show x cannot = 3, just to make sure that you’re not dealing with that undefined number.

pemdas

Parentheses Exponents Multiply Divide Add Subtract.

1. Work everything in parentheses.

2. Calculate all exponents.

3. Multiply and divide, from left to right.

4. Add and subtract, from left to right.

taking per-cents

Taking the percent of a number is simple. To turn a number into a percent, simply move the decimal point two spaces to the right and add the % symbol.

You can also turn a percent into a decimal by moving the decimal point two spaces to the left and dropping the % symbol.

To take the percent of a percent, simply multiply the percents, or convert them back to fractions or decimals and then multiply.