The divisibility rule for 9 is quite straightforward and handy for quickly checking whether a number is divisible by 9 without having to perform full division. According to this rule, a number is divisible by 9 if the sum of its digits is also divisible by 9.
Here’s how you can apply this rule:
- Add the digits of the number together. For example, if you have the number 783, you would add 7 + 8 + 3, which equals 18.
- Check if the sum is divisible by 9. Continuing with our example, the sum is 18. Since 18 is divisible by 9 (as 18 ÷ 9 = 2), the original number 783 is also divisible by 9.
This rule works for any number, whether it’s a single-digit, double-digit, or larger number. For example:
- For the number 234: 2 + 3 + 4 = 9, which is divisible by 9, so 234 is divisible by 9.
- For the number 106: 1 + 0 + 6 = 7, which is not divisible by 9, so 106 is not divisible by 9.
This rule is especially useful in mathematics and mental calculations, allowing for quick assessments without needing a calculator. So next time you’re quickly analyzing a number, just remember to sum the digits and check for divisibility by 9!