# Math facts for GRE

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1. even + even = even * even =
odd + odd = odd * odd =
even + odd = even * odd =
• even + even = even even * even = even
• odd + odd = even odd * odd = odd
• even + odd = odd even * odd = even
2. prime numbers through 30
2, 3, 5, 7, 11, 13, 17, 19, 23, 29
3. divisibility
• by 3 if sum of digits = 3
• by 4 if last two digits of the number are divisible by 4
• by 5 if it ends in 0 or 5
• by 6 if its divisible by both 2 and 3
• by 8 if the last 3 digits form a number divisible by 8
• by 9 if the sum of the gidits is divisible by 9
4. Rules of Exponents
a2 = a * a

a2 * a3 = a2+3 = a5

(a2)3 = a6

a2/a3 = a2-3 = a-1 = 1/a

1512 - 1511 = 1511(15-1) = 1511(14)
5. Rules of Square Roots
• can mult and divide square roots by each other
• can only add/subtract intigers in fromt of root if its the SAME root
• on GRE square root only includes the positive answer, but can square neg numbers to equal positive number
6. square root of 2 =

square root of 3 =
square root of 2 = 1.4

square root of 3 = 1.7