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Useful Mathematics Tricks: Division, Multiplication and More

Division

  • A number will be divisible by 3 if the sum of all the digits is a multiple of 3.  For example, 35,431,452 is divisible by 3 as 3 + 5 + 4 + 3 + 1 + 4 + 5 + 2 = 27 and 27 is divisible by 3.

  • A number will be divisible by 4 if its last two digits is divisible by 4.  For example, 4,349,898,548 is divisible by 4 as the last two digits is 48 and 48 is divisible by 4 (Note: if the last 2 digits are 00, the number is divisible by 4 as it is a multiple of 100 and 100 is divisible by 4).

  • A number will be divisible by 9 if the sum of all the digits is a multiple of 9.  For example, 53,438,652 is divisible by 9 as 5 + 3 + 4 + 3 + 8 + 6 + 5 + 2 = 36 and 36 is divisible by 9.

Multiplication

  • To calculate the square of a 2-digit number ending in 5, simply multiply the first digit by the next consecutive number and put 25 as the last two digits.  For example, 25 x 25 = (2x3)25 = 625, 35 x 35 = (3x4)25 = 1225.

  • To calculate the multiplication of two 2-digits numbers from 11 to 19, you can follow the steps below:

1. Add the ones digit of the first number to the first 2-digit number,

2. Put one zero to the result of #1,

3. Multiply the ones digit numbers,

4. Add the result of #3 to #2.

 

Example: 

 

To multiply 17 and 12.

 

1. Add 7 to 12, we get 19

2. Put one zero to 19, we get 190,

3. Multiply the ones digit numbers, we have 7x2 = 14,

4. Add 14 to 190.  The answer is 204.

 

Find out more tricks from our book

Prime Number Table

Below is the table of the first 30 prime numbers. You can print it  in memorizing the prime numbers.

 

Print this table

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

101

103

107

109

113

Multiplication Table

Below are two multiplication tables, one in words and one in numbers.  You can print them out to assist your children in memorizing them.

Print this table

Two-One Two

Three-One Three

Four-One Four

Five-One Five

Six-One Six

Seven-One Seven

Eight-One Eight

Nine-One Nine

Two-Two Four

Three-Two Six

Four-Two Eight

Five-Two Ten

Six-Two Twelve

Seven-Two Fourteen

Eight-Two Sixteen

Nine-Two Eighteen

Two-Three Six

Three-Three Nine

Four-Three Twelve

Five-Three Fifteen

Six-Three Eighteen

Seven-Three Twenty One

Eight-Three Twenty Four

Nine-Three Twenty Seven

Two-Four Eight

Three-Four Twelve

Four-Four Sixteen

Five-Four Twenty

Six-Four Twenty Four

Seven-Four Twenty Eight

Eight-Four Thirty Two

Nine-Four Thirty Six

Two-Five Ten

Three-Five Fifteen

Four-Five Twenty

Five-Five Twenty Five

Six-Five Thirty

Seven-Five Thirty Five

Eight-Five Forty

Nine-Five Forty Five

Two-Six Twelve

Three-Six Eighteen

Four-Six Twenty Four

Five-Six Thirty

Six-Six Thirty Six

Seven-Six Forty Two

Eight-Six Forty Eight

Nine-Six Fifty Four

Two-Seven Fourteen

Three-Seven Twenty One

Four-Seven Twenty Eight

Five-Seven Thirty Five

Six-Seven Forty Two

Seven-Seven Forty Nine

Eight-Seven Fifty Six

Nine-Seven Sixty Three

Two-Eight Sixteen

Three-Eight Twenty Four

Four-Eight Thirty Two

Five-Eight Forty

Six-Eight Forty Eight

Seven-Eight Fifty Six

Eight-Eight Sixty Four

Nine-Eight Seventy Two

Two-Nine Eighteen

Three-Nine Twenty Seven

Four-Nine Thirty Six

Five-Nine Forty Five

Six-Nine Fifty Four

Seven-Nine Sixty Three

Eight-Nine Seventy Two

Nine-Nine Eighty One

Two-Ten Twenty

Three-Ten Thirty

Four-Ten Forty

Five-Ten Fifty

Six-Ten Sixty

Seven-Ten Seventy

Eight-Ten Eighty

Nine-Ten Ninety

 

Print this table

2x1 = 2

3x1 = 3

4x1 = 4

5x1 = 5

6x1 = 6

7x1 = 7

8x1 = 8

9x1 = 9

2x2 = 4

3x2 = 6

4x2 = 8

5x2 = 10

6x2 = 12

7x2 = 14

8x2 = 16

9x2 = 18

2x3 = 6

3x3 = 9

4x3 = 12

5x3 = 15

6x3 = 18

7x3 = 21

8x3 = 24

9x3 = 27

2x4 = 8

3x4 = 12

4x4 = 16

5x4 = 20

6x4 = 24

7x4 = 28

8x4 = 32

9x4 = 36

2x5 = 10

3x5 = 15

4x5 = 20

5x5 = 25

6x5 = 30

7x5 = 35

8x5 = 40

9x5 = 45

2x6 = 12

3x6 = 18

4x6 = 24

5x6 = 30

6x6 = 36

7x6 = 42

8x6 = 48

9x6 = 54

2x7 = 14

3x7 = 21

4x7 = 28

5x7 = 35

6x7 = 42

7x7 = 49

8x7 = 56

9x7 = 63

2x8 = 16

3x8 = 24

4x8 = 32

5x8 = 40

6x8 = 48

7x8 = 56

8x8 = 64

9x8 = 72

2x9 = 18

3x9 = 27

4x9 = 36

5x9 = 45

6x9 = 54

7x9 = 63

8x9 = 72

9x9 = 81

2x10 = 20

3x10 = 30

4x10 = 40

5x10 = 50

6x10 = 60

7x10 = 70

8x10 = 80

9x10 = 90

 

 

   

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