What is the divisibillity rule of 3?

The divisibility rule of 3 states that a number is divisible by 3 if the sum of its digits is also divisible by 3. For example, to determine if 123 is divisible by 3, you would add 1 + 2 + 3, which equals 6. Since 6 is divisible by 3, the original number 123 is also divisible by 3.