# GRE Math Formulas to Know

## 27 terms

### Percentages General Formula

Percent x Whole = Part

### Percentages: % Increase

(Amount of Increase/ Original whole ) x 100%

### Percentages: % Decrease

(Amount of Decrease/ Original Whole) x 100%

### Percentages: New Whole

New Whole = Original Whole + or - Amount of Change

10% = 1/10
20% = 2/10 = 1/5
30% = 3/10
40% = 4/10 = 2/5
50% = 5/10 = 1/2
60% = 6/10 = 3/5
70% = 7/10
80% = 8/10 = 4/5
90% = 9/10
100% = 10/10 = 1

### Percentages: Out of 8

12-1/2% = 1/8
25% = 2/8 = 1/4
37-1/2% = 3/8
50% = 4/8 = 2/4 = 1/2
62-1/2% = 5/8
75% = 6/8 = 3/4
87-1/2% = 7/8

### Percentages: Out of 6

16-2/3% = 1/6
33-1/3% = 2/6 = 1/3
50% = 3/6 = 1/2
66-2/3% = 4/6 = 2/3
88-1/3% = 5/6

5% = 1/20
20% = 1/5

...

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### Acute Angle

an angle that is less than 90°

### Right Angle

an angle that 90°

### Obtuse Angle

an angle that is greater than 90° but less than 180°

### Straight Angle

an angle that is 180° exactly

### Reflex Angle

an angle that is greater than 180°

A^2

AB

BH

H/2 (b1 + b2)

Pi (r^2)

Pi (r1*r2)

### ...

triangle = (1/2) b h

negative b plus or minus the square root of b squared minus 4ac all over 2a.

D= Rate x Time

### Simple Interest Formula

Interest = principal x rate x time

*RATE must be expressed as a decimal point
*TIME must be expressed in years

### Amount of Investment Formula

To compute the amount, A, of an investment, P, at the end of T years, at an annual rate of R:

A = P (1 + RT)

### Compound Interest Formula

A = P ( 1 + R/C)^TC

A = AMOUNT of investment
P = PRINCIPLE amount invested
R = RATE of interest
C = the number of times compounded annually
T = TIME in years