Is 684 divisble by 3

Answer 1

Sum of digits is divisible by three so yes.

You can check if a number is divisible by 3 (without actually doing the division), by adding up the digits. If that sum is divisible by 3 then the original number is divisible by 3:

6 + 8 + 4 = 18 (which is divisible by 3; if not sure add again: 1 + 8 = 9, yes)

You'll have to 'memorize' that 3, 6 & 9 are divisible by 3.