The GMAT Forum

These formulae's is sort of comprehensive guide for things you should know before attempting the GMAT math ps.

1. Circles

Circumference = 2 * Pi * R where R = Radius or

= Π * D where D = Diameter = 2 * R

Area = Π * R²

The area of a circle is 36. What is the diameter of the circle?

36 = Π * R² so R = 6 / (Square root of Π)

so D = (12 * Square root of Π)/Π

The radius of a circle is 10. What is the circumference of the circle?

Circumference = 2 * Π * R

= 20 * Pi

What formula do you use to find the ratio of the arcs, sectors, etc. of a circle?

x/360 = arc length/circumference = area of sector/area

where x is the degree measure of the angle

2. Perfect Squares

List all the perfect squares from 0 to 100
0 (don't forget 0!), 1, 4, 9, 16, 25, 36, 49, 64, 81, 100

3. Odds and Evens

Odd + Odd = Even

Odd * Even = Even

Even - Even = Even

Even/Odd = Even (or decimal)

Even * Even = Even

Odd + Even = Odd

Odd - Odd = Even

Odd/Odd = Odd (or decimal)

4. Least Common Multiples

What is the least common multiple of 15 and 24?

15 = 3 * 5 and 24 = 2 * 2 * 2 * 3,

Eliminate one of each of the common factors (3) and multiply the rest of the prime factors, LCM = 120

What is the least common multiple of 12 and 30?

12 = 2 * 2 * 3 and 30 = 2 * 3 * 5,

Follow the same procedure as above, eliminate 2 & 3, LCM = 60

5. Common Percent Equivalencies

Decimals to Fractions	Fractions to Decimals
0.4 = 2/5 0.875 = 7/8 0.167 = 1/6 0.85 = 17/20 0.375 = 3/8	5/8 = 0.625 2/40 = 0.05 5/6 = 0.833 3/5 = 0.6 2/16 = 0.125

6. Distance Problems (Distance, Rate & Time)

Distance = Rate * Time

Rate = Distance/Time

Time = Distance/Rate