Which of the following number is divisible by both 3 and 9?
A number is divisible by 3 and 9 if the sum of the digits is divisible by 3 and 9 respectively.
192
Sum of the digits = 1 + 9 + 2 = 12
12 is divisible by 3 but not by 9. Hence, 192 is divisible by 3 but not divisible by 9.
720
Sum of the digits = 7 + 2 + 0 = 9
9 is divisible by both 3 and 9. Hence, 720 is divisible by both 3 and 9.
285
Sum of the digits = 2 + 8 + 5 = 15
15 is divisible by 3 but not by 9. Hence, 285 is divisible by 3 but not divisible by 9.
2398
Sum of the digits = 2 + 3 + 9 + 8 = 22
22 is not divisible by both 3 and 9. Hence, 2398 is not divisible by both 3 and 9.