Question

How many positive integers less than 1000 have the property that the sum of the
digits of each such number is divisible by 7 and the number itself is divisible by 3?

Answer 1

The sum of the digits must be divisible both by 7 and 3 i.e. the sum of digits should be divisible by 21.
The max. sum of digits of a 3 digit no. can be 9+9+9=27
So we need to find only 3digit no.s whose sum of digits comes out to be 21.
U can then find out possibilities,i.e.
9+9+3
9+8+4
9+7+6
..
..
..
.......in the following manner and u would get the answer 28