Flashcards in Arithmetic Tricks Deck (55):

1

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

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

2

## 225

### 15 squared

3

## 121

### 11 squared

4

## 400

### 20 squared

5

## 625

### 25 squared

6

## 169

### 13 squared

7

## 900

### 30 squared

8

## 196

### 14 squared

9

## 125

### 5 cubed

10

## 8

### 2 cubed

11

## 216

### 6 cubed

12

## 27

### 3 cubed

13

## 1000

### 10 cubed

14

## 64

### 4 cubed

15

## 4ˆ4

### 256

16

## 3ˆ3

### 27

17

## 4ˆ3

### 64

18

## 5ˆ3

### 125

19

## 2ˆ4

### 16

20

## 3ˆ4

### 81

21

## 4ˆ4

### 256

22

## 5ˆ4

### 625

23

## 2ˆ5

### 32

24

## 3ˆ5

### 243

25

## 2ˆ6

### 64

26

## Square root of 1

### 1

27

## Square root of 2

### 1.4

28

## Square root of 3

### 1.7

29

## Square root of 5

### 2.2

30

## Square root of 6

### 2.4

31

## Square root of 7

### 2.6

32

## Square root of 8

### 2.8

33

## Square root of 10

### 3.2

34

## > sq. root 4 and < sq. root 10

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

35

## < sq. root 4

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

36

## 1/8 =

### 0.125

37

## 1/11

### 0.09090909090909

38

## 1/6=

### 0.16161616161616...

39

## 1/9=

### 0.111111

40

## 1/99=

### 0.0101010101010101

41

## 1/4=

### 0.25

42

## 1/7=

### Aprox. 0.14

43

## To multiply or divide a number by 4

### DOUBLE or HALVE it 2x

44

## To multiply or divide a number by 8

### DOUBLE or HALVE it 3x

45

## Multiplying by 9

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

46

## Multiplying by 11

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

47

## Multiplying and dividing by 5

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

(23*5 = (23*10)/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)

48

## Subtraction by addition ! GO

###
Number line

OR

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

49

## To easily get 15% of a number

###
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)

50

## To get 1% of a number

###
Slide the decimal point TWO spots to the left

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

51

## Divisibility rules for 8

### Last 3 digits can be cut in half 3x

52

## Divisibility rules for 3

### Sum if its digits is divisible by 3

53

## Divisibility rules for 9

### Sum of its digits is divisible by 9

54

## Divisibility rules for 6

### If divisible by 2 and 3

55