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Divisibility Tests

The following are some shortcuts for deciding whether a given integer is divisible by 2 , 3 , 4 , 5 , 6 , 8 , 9 or 10 .

Divisibility by 2

An integer is divisible by 2 if its last digit is 0 , 2 , 4 , 6 or 8 . (In other words, if it's even.)

Example:

754 is divisible by 2 , since its last digit is 4 .

8267 is not divisible by 2 , since its last digit is not one of 0 , 2 , 4 , 6 or 8 .

Divisibility by 3

An integer is divisible by 3 if the sum of its digits is divisible by 3 .

Example:

747 is divisible by 3 , since

7 + 4 + 7 = 18 ,

and 18 is divisible by 3 ( 6 × 3 = 18 ).

2389 is not divisible by 3 , since

2 + 3 + 8 + 9 = 22 ,

and 22 not divisible by 3 .

You can use this rule twice or more times in succession for large numbers. For example, to test 965787 for divisibility by 3 , first add the digits:

9 + 6 + 5 + 7 + 8 + 7 = 42

If you're not sure about 42 , add the digits again.

4 + 2 = 6

6 is definitely divisible by 3 . So, 965787 is also.

Divisibility by 4

An integer is divisible by 4 if the last two digits are divisible by 4 . (This is because 4 goes evenly into 100 .)

Example:

7508 is divisible by 4 , since 08 or 8 is divisible by 4 .

8437 is not divisible by 4 , since 37 is not divisible by 4 .

Divisibility by 5

An integer is divisible by 5 if the last digit is either 0 or 5 .

Example:

9375 is divisible by 5 , since the last digit is a 5 .

8417 is not divisible by 5 , since the last digit is not a 0 or a 5 .

Divisibility by 6

An integer is divisible by 6 if it is divisible by 2 and divisible by 3 .

Example:

966 is divisible by 6 , since:

  • It's divisible by 2 (the last digit is 6 )
  • It's divisible by 3 ( 9 + 6 + 6 = 21 , which is divisible by 3 ).

268 is not divisible by 6 , since:

  • It's divisible by 2 (the last digit is 8 )
  • But it's not divisible by 3 ( 2 + 6 + 8 = 16 , which is not divisible by 3 ).

 

Divisibility by 7

Unfortunately, there is no good test for divisibility by 7 .

Divisibility by 8

An integer is divisible by 8 if the last three digits are divisible by 8 . (This is because 8 goes evenly into 1000 .)

Example:

56104 is divisible by 8 , since 104 is divisible by 8

( 13 × 8 = 104 ).

29027 is not divisible by 8 , since 27 is not divisible by 8 .

Divisibility by 9

An integer is divisible by 9 if the sum of the digits is divisible by 9 .

Example:

76653 is divisible by 9 , since:

7 + 6 + 6 + 5 + 3 = 27 ,

and 27 is divisible by 9 .

29027 is not divisible by 9 , since:

2 + 9 + 0 + 2 + 7 = 20 ,

and 20 is not divisible by 9 .

Divisibility by 10

An integer is divisible by 10 if the last digit is 0

Example:

46090 is divisible by 10 , since the last digit is 0 .

29027 is not divisible by 10 , since the last digit is not 0 .