Divisibility Tricks for Learning Math

$Divisibility Tricks for Learning Math$

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A great way to enhance student learning in mathematics is to use tricks. Luckily, if you are teaching division, there are a lot of math tricks to choose from.

Dividing by 2

All even numbers are divisible by 2. E.g., all numbers ending in 0, 2, 4, 6, or 8.

Dividing by 3

Add up all the digits in the number.
Find out what the sum is. If the sum is divisible by 3, so is the number.
For example: 12123 (1+2+1+2+3=9) 9 is divisible by 3, therefore 12123 is too!

Dividing by 4

Are the last two digits in your number divisible by 4?
If so, the number is too!
For example: 358912 ends in 12 which is divisible by 4, and so is 358912.

Dividing by 5

Numbers ending in 5 or 0 are always divisible by 5.

Dividing by 6

If the number is divisible by 2 and 3, it is also divisible by 6.

Dividing by 7

First Test:

Take the last digit in a number.
Double and subtract the last digit in your number from the rest of the digits.
Repeat the process for larger numbers.
Example: Take 357. Double the 7 to get 14. Subtract 14 from 35 to get 21, which is divisible by 7, and we can now say that 357 is divisible by 7.

Second Test:

Take the number and multiply each digit beginning on the right-hand side (ones) by 1, 3, 2, 6, 4, 5. Repeat this sequence as necessary.
Add the products.
If the sum is divisible by 7, so is your number.
Example: Is 2016 divisible by 7?
6(1) + 1(3) + 0(2) + 2(6) = 21
21 is divisible by 7, and we can now say that 2016 is also divisible by 7.

Dividing by 8

This one's not as easy. If the last 3 digits are divisible by 8, so is the entire number.
Example: 6008. The last 3 digits are divisible by 8, meaning 6008 is as well.