Arithmetic Tricks

Question 1

Find the multiple of two numbers separated by 2 (e.g., 12 and 14)

Answer 1

square the number in the middle and subtract 1 (e.g., 13 x 13 = 169-1 = 168)

Question 2

225

Answer 2

15 squared

Question 3

121

Answer 3

11 squared

Question 4

400

Answer 4

20 squared

Question 5

625

Answer 5

25 squared

Question 6

169

Answer 6

13 squared

Question 7

900

Answer 7

30 squared

Question 8

196

Answer 8

14 squared

Question 9

125

Answer 9

5 cubed

Question 10

8

Answer 10

2 cubed

Question 11

216

Answer 11

6 cubed

Question 12

27

Answer 12

3 cubed

Question 13

1000

Answer 13

10 cubed

Question 14

64

Answer 14

4 cubed

Question 15

4ˆ4

Answer 15

256

Question 16

3ˆ3

Answer 16

27

Question 17

4ˆ3

Answer 17

64

Question 18

5ˆ3

Answer 18

125

Question 19

2ˆ4

Answer 19

16

Question 20

3ˆ4

Answer 20

81

Question 21

4ˆ4

Answer 21

256

Question 22

5ˆ4

Answer 22

625

Question 23

2ˆ5

Answer 23

32

Question 24

3ˆ5

Answer 24

243

Question 25

2ˆ6

Answer 25

64

Question 26

Square root of 1

Answer 26

1

Question 27

Square root of 2

Answer 27

1.4

Question 28

Square root of 3

Answer 28

1.7

Question 29

Square root of 5

Answer 29

2.2

Question 30

Square root of 6

Answer 30

2.4

Question 31

Square root of 7

Answer 31

2.6

Question 32

Square root of 8

Answer 32

2.8

Question 33

Square root of 10

Answer 33

3.2

Question 34

> sq. root 4 and < sq. root 10

Answer 34

Add 0.2 (sq root 4=2, sq root 5 = 2.2, sq. root 6 = 2.4, etc.)

Question 35

< sq. root 4

Answer 35

Subtract 0.3 (sq. root 4 = 2, sq. root = 1.7, etc.)

Question 36

1/8 =

Answer 36

0.125

Question 37

1/11

Answer 37

0.09090909090909

Question 38

1/6=

Answer 38

0.16161616161616…

Question 39

1/9=

Answer 39

0.111111

Question 40

1/99=

Answer 40

0.0101010101010101

Question 41

1/4=

Answer 41

0.25

Question 42

1/7=

Answer 42

Aprox. 0.14

Question 43

To multiply or divide a number by 4

Answer 43

DOUBLE or HALVE it 2x

Question 44

To multiply or divide a number by 8

Answer 44

DOUBLE or HALVE it 3x

Question 45

Multiplying by 9

Answer 45

MULTIPLY by 10, then subtract original number (23 x 9 = 23*10 - 23 = 230 - 23 = 207

Question 46

Multiplying by 11

Answer 46

Multiply by 10 and ADD the original number number (45 x 11 = 45 x 10 + 45 = 450 + 45 = 495)

Question 47

Multiplying and dividing by 5

Answer 47

Multiply the number by 10, then divide the answer by 2

(235 = (2310)/2 = 230/2 = 115)
OR

Divide the number by 10, then multiply by 2
(96/5 = (96/10) x 2 = 9.6 x2 = 19.2)

Question 48

Subtraction by addition ! GO

Answer 48

Number line
OR
Guess (X + WHAT NUMBER gets me close to Y?)

Question 49

To easily get 15% of a number

Answer 49

First get 10% (slide decimal point one spot to left, 10% of 100 is 10, 10% of 53 is 5.3)

Then get 5% by taking half of 10% (5% of 53 = 2.6ish)

Then add (5.3 + 2.6 = 7.9 = 15% of 53)

Question 50

To get 1% of a number

Answer 50

Slide the decimal point TWO spots to the left

1% of 34 = 0.34, 1% of 0.07 = 0.0007

Question 51

Divisibility rules for 8

Answer 51

Last 3 digits can be cut in half 3x

Question 52

Divisibility rules for 3

Answer 52

Sum if its digits is divisible by 3

Question 53

Divisibility rules for 9

Answer 53

Sum of its digits is divisible by 9

Question 54

Divisibility rules for 6

Answer 54

If divisible by 2 and 3

Question 55

Divisibility rules for 4

Answer 55

If it’s last 2 digits can be cut in half 2x