Mathnasium #MathTricks: Divisibility (Rule for 3s)

A number is divisible by 3 if the sum of the digits is divisible by 3.

To determine if the number 87 is divisible by 3, we find the sum of its digits. Eight plus seven gives us a final sum of fifteen. Fifteen is divisible by 3. So,

87 is divisible by 3.

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