Answer and Explanation:
To find out if a number is divisible by 3, we must add the numbers of that number. If the result of the sum is a number divisible by 3, then that means that the original number is divisible by 3:
215 - adding the numbers: 2 + 1 + 5 = 8 (8 is not divisible by 3, so 215 is not divisible by 3).
649 - Adding the numbers: 6 + 4 + 9 = 19 (19 is not divisible by 3, so 649 is not divisible by 3).
When a number is divisible by 2, or by 3, it is also divisible by 6. We already know that the numbers above are not divisible by 3. Even numbers are the numbers that can be divided by 2, the numbers above are not even, which indicates that they are not divisible by 2, nor by 6, consequently.
To find out if the number is divisible by 9, the sums of the numbers in that number must be divisible by 9.
215 - adding the numbers: 2 + 1 + 5 = 8 (7 is not divisible by 9, so 215 is not divisible by 9)
649 - Adding the numbers: 6 + 4 + 9 = 19 (19 is not divisible by 9, so 649 is not divisible by 9).
