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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! ... |

Created by:
qiguai