Divisibility Rules
Easily test if one number can be evenly divided by another
Divisible By
"Divisible By" means "If you divide one number by another, is the result a whole number?"
Example, 14 is divisible by 7, because 14÷7 = 2 exactly
But 15 is not divisible by 7, because 15÷7 = 2 1/7 (i.e., the result is not a whole number)
The Divisibility Rules
These rules let you test if one number can be evenly divided by another, without having to do too much calculation!
A number is
divisible by: |
If: |
Example: |
| 2 |
The last digit is even (0,2,4,6,8) |
128 is
129 is not |
| 3 |
The sum of the digits is divisible by 3 |
381 (3+8+1=12, and 12÷3 = 4) Yes
217 (2+1+7=10, and 10÷3 = 3 1/3) No |
| 4 |
The last 2 digits are divisible by 4 |
1312 is (12÷4=3)
7019 is not |
| 5 |
The last digit is 0 or 5 |
175 is
809 is not |
| 6 |
The number is divisible by both 2 and 3 |
114 (it is even, and 1+1+4=6 and 6÷3 = 2) Yes
308 (it is even, but 3+0+8=11 and 11÷3 = 3 2/3) No |
| 7 |
If you double the last digit and subtract it from the rest of the number and
the answer is:
(Note: you can apply this rule to that answer again if you want) |
672 (Double 2 is 4, 67-4=63, and 63÷7=9) Yes
905 (Double 5 is 10, 90-10=80, and 80÷7=11 3/7) No
|
| 8 |
The last three digits are divisible by 8 |
109816 (816÷8=102) Yes
216302 (302÷8=37 3/4) No |
| 9 |
The sum of the digits is divisible by 9
(Note: you can apply this rule to that answer again if you want) |
1629 (1+6+2+9=18, and again, 1+8=9) Yes
2013 (2+0+1+3=6) No |
| 10 |
The number ends in 0 |
220 is
221 is not |
| 11 |
If you sum every second digit and then subtract all other digits and the answer is:
|
1364 ((3+4) - (1+6) = 0) Yes
3729 ((7+9) - (3+2) = 11) Yes
25176 ((5+7) - (2+1+6) = 3) No |
| 12 |
The number is divisible by both 3 and 4 |
648 (6+4+8=18 and 18÷3=6, also 48÷4=12) Yes
916 (9+1+6=16, 16÷3= 5 1/3) No |
There are lots more! Not only are there divisibility tests for larger numbers, but there are more tests for the numbers we have shown.
Factors Can Be Useful
Factors are the numbers you multiply to get another number:
This can be useful, because:
When a number is divisible by another number ...
... then it is also divisible by each of the factors of that number.
Example: If a number is divisible by 6, it is also divisible by 2 and 3
Example: If a number is divisible by 12, it is also divisible by 2, 3, 4 and 6
|
Home
