How many numbers divisible by 3 or 4 between 100 and 999 inclusive?

The solution for the problem is:

There are 1000 div 4 - 100 div 4 = 225 numbers divisible by 4 and 1000 div 3 - 100 div 3 = 333 - 33 = 300 numbers divisible by 3. On the other hand, we have calculated numbers divisible by 12 in those two groups. There are 1000 div 12 - 100 div 12 = 83 - 8 = 75 numbers like that. In conclusion, there are 225 + 300 - 75 = 450 numbers divisible by 3 or 4.