GRE Math Formulas

compound interest

final balance= principal x (1+interest rate/c)^(time x c) c= how many times it was compounded in a year

Simple Interest Formula

interest= principle x rate x time

how to find the sum of all the angles of a polygon and one angle measure of a regular polygon

sum of the interior angles: (n-2)x180 degree measure of one angle in a regular polygon with n sides ((n-2)x180)/n

Area of a trapezoid

(average of parallel sides) x (height)

area of a triangle

1/2 x base x height

Length of an arc

Length of an Arc = (central angle/360) x 2πr

volume of a cyclinder

area of the base x height or otherwise pi x r^2 x height

Area of a parallelogram

base x height

Area of a sector

x°/360 times (∏r²), where x is the degrees in the angle

How to solve a remainders problem

-Pick a number that fits the given conditions and see what happens. -Ex: When n is divided by 7, the remainder is 5. What is the remainder when 2n is divided by 7? -Find a number that leaves a remainder of 5 when divided by 7. You can find such a number by taking any multiple of 7 and adding 5 to it. A good choice would be 12. -If n=12, then 2n = 24, which when divided by 7 leaves a remainder of 3

how to use a ratio to determine an actual number

-Set up a proportion using the given ratio -Ex: The ratio of bogs to girls is 3 to 4. If there are 135 boys, how many girls are there? So, 3/4 = 135/g; Solve and g = 180

how to find the sum of consecutive numbers

-Sum = (average) x (number of terms) -Ex: What is the sum of the integers from 10 through 50, inclusive? average: 10 + 50 / 2 = 30; number of terms: 50 - 10 + 1 = 41; sum: 30 x 41 = 1230

circumfrence of a circle

2πr or πd

area of a circle

A=πr²