Question

Use the divisibility tests to determine whether the following numbers are divisible by 2, 3, 4, 5, 6, 9 or 11.

(9) 720

Answer 1

We can observe that the digit in the units place is 0.
If a number has either 0 or 5 in its units place, then the number is divisible by 5; and if a number has 0, 2, 4, 6 or 8 in its units place, then the number is divisible by 2. So, the number 720 is divisible by both 2 and 5.

The sum of the digits 7, 2 and 0 is 9, which is divisible by both 3 and 9.
If the sum of all the digits in a number is divisible by 3 and 9, then the number is divisible by 3 and 9. So, the number 720 is divisible by both 3 and 9.

If a number is divisible by both 2 and 3, then the number is divisible by 6. So, the number 720 is divisible by 6.

The number formed by the digits in the tens and units places is 20, which is divisible by 4.
If the number formed by the digits in the tens and units places of a number is divisible by 4, then the number is divisible by 4. So, the number 720 is divisible by 4.

Hence, the number 720 is divisible by 2, 3, 4, 5, 6 and 9.