If a number is divisible by 9, it must be divisible by 3. ?
Since 9 is divisible by 3, every number divisible by 9 will be also be divisible by 3. This happens because in the divisibilty test formula of 9, the sum of the digits should be divisible by 9. If this sum is divisible by 9, it automatically is divisible by 3 since 3 is a factor of 9.
