The rule of 3 and 9 is a simple divisibility rule that helps determine whether a number is divisible by 3 or 9.
To check if a number is divisible by 3:
- Add up all the digits in the number.
- If the sum of the digits is divisible by 3, then the original number is also divisible by 3.
For example:
- The number 123 is divisible by 3 because 1 + 2 + 3 = 6, and 6 is divisible by 3.
To check if a number is divisible by 9:
- Add up all the digits in the number.
- If the sum of the digits is divisible by 9, then the original number is also divisible by 9.
For example:
- The number 729 is divisible by 9 because 7 + 2 + 9 = 18, and 18 is divisible by 9.
