Answer:
Divide by Three Trick
This is a fun trick. If the sum of the digits in a number can be divided by three, then the number can as well.
Examples:
1) The number 12. The digits 1+2=3 and 12 ÷ 3 = 4.
2) The number 15. The digits 1+5 = 6, which is divisible by 3. It turns out that 15 ÷ 3 = 5