Question

Give five examples of numbers, each one of which is divisible by 3 but not divisible by 9.

Answer 1

For a number to be divisible by 3, the sum of the digits should be divisible by 3.
And for the number to be divisible by 9, the sum of the digits should be divisible by 9.
Let us take the number 21.
Sum of the digits is 2 + 1 = 3, which is divisible by 3 but not by 9. Hence, 21 is divisible by 3 not by 9.
Similarly, lets check the number 24. Here, 2 + 4 = 6. This is divisible by 3 not by 9.
The number 30 will be divisible by 3 not by 9 as 3 + 0 = 3.
The number 33 will give 3 + 3 = 6, which is divisible by 3 not by 9.
Also 39 has the digits 3 + 9 = 12, which is divisible by 3 not by 9.
Hence, the numbers 21, 24, 30, 33 and 39 are divisible by 3 not by 9.