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GMAT Math
Term | Definition |
---|---|
Primes less than 20 | 2, 3, 5, 7, 11, 13, 17, 19 |
Primes greater than 20 | 23, 29, 31, 37, 41, 43, 47 |
Divisibility by 3 | sum of digits divisible by 3 |
divisibility by 4 | last 2 digits divisible by 4 |
divisibility by 7 | difference b/t units digit x 2 and rest of number divisible by 7 |
divisibility by 8 | last 3 digits divisible by 8 |
divisibility by 9 | sum of digits divisible by 9 |
divisibility by 11 | difference between odd digits places summed and even digits places summed divisible by 11 |
Simple interest | P(1+rt) |
compound interest | P(1+r)^t |
interest: p or principal | starting investment amount |
interest: r | interest rate per time period |
interest: t | number of time periods interest is accrued over |
14^2 | 196 |
16^2 | 256 |
17^2 | 289 |
18^2 | 324 |
19^2 | 361 |
a^2 - b^2 | (a+b)(a-b) |
a^2 + 2ab + b^2 | (a+b)^2 |
a^2 - 2ab + b^2 | (a-b)^2 |
odd + odd | even |
even + even | even |
odd + even | odd |
odd x odd | odd |
even x even | even |
odd x even | even |
odd ^ positive | odd |
even ^ positive | even |
first three pythagorean triples | 3-4-5, 5-12-13, 8-15-17 |
lengths of isosceles right triangle | 1-1-sqrt2 |
lengths of 30-60-90 triangle | 1-2-sqrt3 |
sum of interior angles of a polygon | 180(n-2) |
diagonal of rectangular prism | l^2 + w^2 + h^2 |
volume of cylinder | pi r^2 h |
surface area of cylinder | 2 pi r^2 + 2 pi r h |
volume of sphere | 4/3 pi r^3 |
surface area of sphere | 4 pi r ^2 |
decimal 1/6 | 0.1666 |
decimal 1/8 | 0.125 |
decimal 1/9 | 0.1111... |
decimal 5/6 | 0.8333... |
decimal 3/8 | 0.375 |
decimal 5/8 | 0.625 |
decimal 7/8 | 0.875 |
decimal 1/11 | 0.090909... |
total time to finish a job (2 people) | (TaTb)/(Ta + Tb) |
total time to finish a job (2+ people) | 1/Tall = 1/Ta + 1/Tb + 1/Tc + ... |
does order matter for combo or permu? | order matters for permutations |
formula for combinations: n choose k (how many combos of k items from n set) | n! / (k! (n-k)!) |
formula for permutations | n! / (n-k)! |
formula for arrangements of repeating elements where rx repeats | n! / r1! r2! ... |