In the first 100 natural numbers, the sum of all numbers divisible by 3 is

In the first 100 natural numbers, the sum of all numbers divisible by 3 is

3(1+2+3+...+32+33)
=3*(1+33)*33/2
=3*34*33/2
=3*33*17
=(100-1)*17
=1700-17
=1683