How to check if a number is divisible by 3?

Given any number, no matter how big, we show how to easily determine if it is divisible by 3 within seconds.

Instructions

Difficulty: Easy

1. Add up the digits in the number to get a new number.
2. If the new number is divisible by 3, then the original number was divisible by 3.
3. If the number you got in step one is still large, then add up the digits of the new number using the step 1 again. This can all be done rather quickly in your head.