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.