If a number has a 9 in the ones place is it always divisible by 3?

No, a number with a 9 in the ones place is not always divisible by 3. For a number to be divisible by 3, the sum of its digits must be divisible by 3, not just the last digit. For example, the number 39 (3 + 9 = 12, which is divisible by 3) is divisible by 3, but the number 29 (2 + 9 = 11, which is not divisible by 3) is not.