Question

Find the sum of all three digit numbers divisible by 4

Answer 1

The numbers which are divisible by 4 and 3, is a multiple of 4*3 i.e.

they are multiple of 12.

the lowest 3 digit  number which is divisible by 12 is 108.

the largest 3 digit  number which is divisible by 12 is 83*12=996 [since 1000/12=83.33] 

let the total number of 3 digit numbers which is divisible by 4 and 3 is n.

therefore 996=108+(n-1)*12

906-108=(n-1)*12

888=(n-1)*12

n-1=888/12=74

n=74+1=75

therefore the sum of the numbers which are divisible by 4 and 3 (i.e. divisible by 12)