GRE Arithmetic
% change #increasing
(New - old) / old
% change #decreasing
(Old - new) / old
0.6% of 800
0.6/100=0.006 0.006(800)=4.8
10^n
10, 100, 1000, 10000
150% of 48
150/100=1.5 1.5(48)=72
15 is 30% of which number
15=.30x x=50
Prime numbers 2-97
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97
2^n
2, 4, 8, 16, 32, 64
Ratio problems
20=d+c ratio is 3:2 =5 20/5=4 sets; so 3(4)=12 and 2(4)=8. 12+8=20 so 8 cats
3^n
3, 9, 27, 81, 243, 729
4^n
4, 16, 64, 256, 1024
40% of 15
40/100 = .4(15)=6
5^n
5, 25, 125, 625, 3125
11 is what percent of 55?
55(x)=11 x=0.2 x=20%
6^n
6, 36, 216, 1296
7^n
7, 49, 343, 2401
8^n
8, 64, 512, 4096
9^n
9, 81, 729, 6561
Even exponent rules
A negative base raised to an even exponent is ALWAYS positive. Ex: (-5)^2 = 25
Odd exponent rules
A negative based raised to an odd exponent is ALWAYS negative. Ex: (-5)^3 = 125
Divisibility rules of 7
Double the last digit and subtract it from a number made by the other digits. The results must be divisible by 7. Ex: 672 (double 2 is 4, 67-4=63, and 63/7=9)
Even/odd rules for addition/subtraction
Even + even = even Even + odd = odd Odd + odd = even
Even and Odd Multiplication rules
Even x even = even Even x odd = even Odd x odd = odd
Divisibility rules of 8
If the last 3 digits is divisible by 8
Divisibility rules of 4
If the last two digits is divisible by 4
Divisibility rules of 6
If the number is divisible by 2 and 3
Divisibility rules of 12
If the number is divisible by 3 and 4
Divisibility rules of 9
If the sum of the digits is divisible by 9
Divisibility Rules of 2
Last digit is 0, 2, 4, 6, or 8
Divisibility rules of 5
ends in 0 or 5
Divisibility rules of 3
if the sum of the digits is divisible by 3