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
- 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.
- 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.
Dividing by 9
- Almost the same rule and dividing by 3. Add up all the digits in the number.
- Find out what the sum is. If the sum is divisible by 9, so is the number.
- For example: 43785 (4+3+7+8+5=27) 27 is divisible by 9, therefore 43785 is too!
Dividing by 10
- If the number ends in a 0, it is divisible by 10.