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# GRE Math

### basic math concepts

Question | Answer |
---|---|

recognize multiples of 3 | sum of digits is a multiple of 3 |

recognize multiples of 4 | sum of digits are a multiple of 4 |

recognize multiples of 6 | sum of digits is a multiple of 3 and last digit is even |

recognize multiples of 9 | sum of digits is a multiple of 9 |

recognize multiples of 12 | sum of digits is a multiple of 3 and last two digits are a multiple of 4 |

prime number | A prime number can be divided, without a remainder, only by itself and by 1. Examples: 2,3,5,7,11,13,17,etc...(note: 1 and 0 are not considered prime numbers) |

composite number | A composite number is defined as any number, greater than 1, that is not prime. |

how to find the least common multiple | To find the least common multiple divide both numbers by the common factors that they share. |

how to find percent change | % change=(amount changed/original whole)*100 |

probability | probability= number of favorable outcomes/total number of possible outcomes |

Simplify polynomials ex. ((3x^2)+5x)(x-1) | ((3x^2)+5x)(x-1)= (3x^2)(x-1)+5x(x-1)= (3x^3)-(3x^2)+(5x^2)-5x= (3x^3)+(2x^2)-5x= |

How to factor the following polynomials: ab+ac (a^2)+2ab+(b^2) (a^2)-2ab+(b^2) (a^2)-(b^2) | ab+ac=a(b+c) (a^2)+2ab+(b^2)=(a+b)^2 (a^2)-2ab+(b^2)=(a-b)^2 (a^2)-(b^2)=(a-b)(a+b) |

When solving for an inequality, when do you flip the sign? | Multiplication or division by a negative number reverses the sign of the inequality |