bono wrote:

We have a set of 900 integers (1000-100). Therefore, we meet an integer that is divisible by 3, 900/3=300 times.

Then, if we look at an array of the integers divisible by 3 {102, 105, 108, 111, 114, 117, 120, 123, 126, 129, 132, 135} we can see that each fifth integer is divisible by 5.

Hence, the number of integers divisible by 5 is 300/5=60

Therefore, the number of integers divisible by 3, but not by 5 is 300-60=240

stolyar, what do you think?

I like the answer and explanation - I would like to change mine to match yours!