Between the numbers 1221 2736 and 45 which of the numbers of visible by both 3 and 9

Among the given numbers, only 2736 and 45 are divisible by both 3 and 9 .

Step-by-step explanation:

We know that an integer is divisible by 3 or 9 iff (if and only if) the sum of it's digits are divisible by 3 or 9 respectively.

Now,

sum of the digits of 1221 = (1 + 2+ 2 + 1)= 6 which is divisible by 3 but not divisible by 9 , hence, 1221 is divisible by 3 but not by 9.

and,

sum of the digits of 2736 = (2+ 7+ 3 + 6)= 18 which is divisible by both 3 and 9 , hence, 2736 is divisible by both 3 and 9.

and,

sum of the digits of 45 = (4 + 5)= 9 which is divisible by both 3 and 9 , hence, 45 is divisible by both 3 and 9.