Divisibility Rules: No, it’s not Cheating!
By Lisa Williams
These rules are useful for kids from the time they start division, on. They keep me from using a calculator and most of the time, I can even work it in my head faster than the calculator because of these rules. I use them most when reducing awkward fractions.
| To Divide by … | |
| 2 | A number is divisible by 2 if it ends in 0 or an even number.Example: 40 divided by 2 = 20 3974 divided by 2 = 1987 |
| 3 | A number is divisible by 3 if the sum of the digits is divisible by 3.Example: 321 add 3+2+1= 6 so 321 divided by 3 = 107 2460 add 2+4+6+0= 12 so 2460 divided by 3 = 820 |
| 4 | A number is divisible by 4 if the last 2 digits are both zeros or if they are divisible by 4.Example: 300 divided by 4 = 75 3548 divided by 4 = 887 |
| 5 | A number is divisible by 5 if it ends in 0 or 5.Example: 25 divided by 5 = 5 400 divided by 5 = 80 |
| 6 | A number is divisible by 6 if it is even and divisble by 3.Example: 246 is even and 2+4+6 = 12 so 246 divided by 6 = 41 |
| 9 | A number is divisible by 9 if the sum of the digits is divisible by 9.Example: 81 add 8 + 1= 9 so 81 divided by 9 = 9 972 add 9+7+2 = 18 so 972 divided by 9 = 18 |
| 10 | A number is divisible by 10 if it ends in 0.Example: 400 divided by 10 = 40 |
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