GMAT 00 - Arithmetic Flashcards
Which quantity is bigger? A) square root 3 + cube root 3 + 4th root 3 B) 5.1
= 5.1 square root 3 = 1.7 (approx) cube root of 3 = smaller than 1.7 4th root of 3 = smaller than cube root of 3 = smaller than 1.7 1.7 + 1.7 + 1.7 = 5.1 since cube root and 4th root are smaller than 1.7, 5.1 is bigger.
108/9 (chunking technique)
= 12 108/9 = (99 + 9)/9 = 99/9 + 9/1 = 11 + 1 = 12
4x7 =
= 28
11x7 =
= 77
8x10 =
= 80
21x11 (arithmetic shortcut)
= 231 21x11 = (20+1) x 11 = (20x11) + 11 = 220 + 11 = 231
1,000 =
10^3
3^4 =
= 81
16x9 (arithmetic shortcut)
= 144 16x9 = 16x10 - 16 = 160 - 16 = 144
4x12 =
= 48
4/9 (decimal equivalent)
= .4444444
165/11
= 15 165/11 = (110 + 55) / 11 = 110/11 + 55/11 = 10 + 5 = 15 – Chunking –
0.0833333 (fraction conversion) =
= 1/12
9x4 =
= 36
4x8 =
= 32
is 405 divisible by 3, 5, and 9?
= Yes 4+0+5 = 9 9 = divisible by 3 9 = divisible by 9 405 = ends in 5 = divisible by 5
12x10 =
= 120
1/99 (decimal conversion) =
= 0.0101010101
17^2 =
= 289
2x11 =
= 22
10x8 =
= 80
Trick: Divide by 8
Cut your number in half three times
9x8 =
= 72
4^3 =
= 64
100 =
= 10^2
322/14 (chunking technique)
= 23 322/14 = (280 + 42)/14 = 280/14 + 42/14 = 20 + 3 = 23
9x6 =
= 54
10^2 =
= 100
Square Root of 5
= 2.2 (approx)
4x2 =
= 8
6x8 =
= 48
256 =
4^4 or 2^8
8x8 =
= 64
142/3 =
= 47 remainder 1 142/3 = (120 + 22)/3 = 120/3 + 22/3 = 40 + 7 remainder 1 = 47 remainder 1
196 =
= 14^2
4x11 =
= 44
is 108 divisible by 3, 4, 6, and 9? (Divisibility Rules)
= Yes 1 + 0 + 8 = 9 9 = divisible by 3 9 = divisible by 9 108 = 08/2 = 04/2 = 02 = Divisible by 4 108 = even = divisible by 2 108 = divisible by 2 and 3 = divisible by 6
Dimensions of a Right Isosceles Triangle
= X : X : X root 2
144 =
= 12^2
4^3 =
= 64
The Fast Fraction Shortcut
1/x + 1/y = (y+x)/xy also works for subtraction 1/x - 1/y = (y-x)/xy
225 =
= 15^2
13^2 =
= 169
6^3 =
= 216
An integer is divisible by 9 if… (Divisibility Rules)
If the sum of its digits is divisible by 9
400 =
= 20^2
Trick: 20% shortcut (or 30% or 40%)
To get 20% of a number, calculate 10% and multiply it by 2 (or 3 for 30% or 4 for 40%)
5x5 =
= 25
10x2 =
= 20
7x8 =
= 56
92/4 (arithmetic shortcut)
= 23 92/4 = (92/2) / 2 = 46/2 = 23
Dimensions of a 30-60-90 Right Triangle
= X : X root 3 : 2x
25^2 =
= 625
11x8 =
= 88
An integer is divisible by 10 if… (Divisibility Rules)
If it ends in a 0
25 =
= 5^2
125 =
5^3
16 =
2^4 or 4^2
20^2 =
= 400
32 =
2^5
11x3 =
= 33
9x11 =
= 99
1/12 (decimal conversion) =
= 0.083333333
30^2 =
= 900
10x6 =
= 60
Definition: A Perfect Cube
A Perfect Cube is a number that results from one number multiplied by itself twice (the square of itself) ex. 125 is a perfect cube (5x5x5 or 5x5^2)
9x12 =
= 108
3x9 =
= 27
289 =
= 17^2
3^2 =
= 9
1/4 (decimal conversion) =
= 0.25
11 x 14 (multiplication trick)
= 154 11x14 = 14 (10 + 1) = 140 + 14 = 154
The Perfect Square Minus 1 Trick
If you know your perfect squares, then you can figure out the total of any numbers multiplied around any perfect square. For example: 6x6 = 36 therefore 5x7 = (6x6 - 1) = 35
3x10 =
= 30
3x4 =
= 12
5x6 =
= 30
2^2 =
= 4
1/9 (decimal conversion) =
= 0.1111111
12x4 =
= 48
19^2 =
= 361
6x3 =
= 18
15^2 (numerical equivalent)
= 225
Trick: 10% shortcut
To get 10% of a number, shift the decimal one space to the left
243 =
3^5
0.09090909 (fraction conversion) =
= 1/11
6x9 =
= 54
12x5 =
= 60
7x5 =
= 35
8x2 =
= 16
1/7 (decimal conversion) =
= 0.14 (approx)
0.1111111 (fraction conversion) =
= 1/9
9x9 =
= 81
1/11 (decimal conversion) =
= 0.09090909
Square Root of 1
= 1
36 =
= 6^2
0.1 (fraction conversion) =
= 1/10
0.125 (fraction conversion) =
= 1/8
If n = 161/7, what is the value of n?
= 23 161/7 = (140 + 21) 7 = 140/7 + 21/7 = 20 + 3 = 23
10x5 =
= 50
is 480 diisible by 3, 6 and 9?
= 3 and 6 = Yes = 9 = No 480 = 4 + 8 = 12 = divisible by 3 = not divisible by 9 480 = even = divisible by 2 480 = divisible by 2 and 3 = divisible by 6
Which of these quantities are greater: A = Square root of 2 + square root of 6 + square root of 8 B = 4
Answer = A A = (approx) 1.4 + 2.4 + 2.8 = 6.6 B = 4 << This is a trap question: you can’t add roots directly >>
256 =
= 16^2
31 x 13 (multiplication trick)
= 403 31x13 = 31(10+3) = 310 + 93 = 403
Does 16x25 = 400?
Answer = Yes 16 = 4x4 (25)(4)(4) = (100)(4) = 400
2x5 =
= 10
3x6 =
= 18
5x1 =
= 5
7x99 (arithmetic shortcut)
= 693 7x99 = 7x100 - 7 = 700 - 7 = 693
11x6 =
= 66
24x5 (arithmetic shortcut)
= 120 24x5 = (20+4) x 5 = 20x5 + 4x5 = 100 + 20 = 120
Does 18 x 9 = 162?
Answer = yes 18 = (9)(2) (9)(2) x 9 = (9)(9)(2) = 81 x 2 = 162
0.33333 (fraction conversion) =
= 1/3
1/3 (decimal conversion) =
= 0.33333
6x6 =
= 36
11x9 =
= 99
5x2 =
= 10
19x21 =
= 399 19x21 = 20x20 - 1 19x21 = 400 - 1 = 399 – Perfect Square Minus 1 Trick –
3^3 =
= 27
Definition: A Perfect Square
A Perfect Square is a number that results from one number multiplied by itself Ex. 25 is a perfect square (5x5)
8 x 17 (multiplication trick)
= 136 8 x 17 = 8 (10 + 7) = 80 + 56 = 136
9x5 =
= 45
5%, 10%, and 15% of 40 (10% shortcut)
= 2, 4, and 6
2^3 =
= 8
361 =
= 19^2
64 =
2^6 or 4^3
2/7 (decimal equivalent)
= .28
2^6 =
= 64
90/5 (arithmetic shortcut)
= 18 90/5 = (18x5)/5 = 18
6x10 =
= 60
5x8 =
= 40