Question

How many numbers from 0 to 999 are not divisible by 5 nor 7?

Answer 1

numbers from 0 to 999 are 1000

Answer 2

The largest multiple of 5 just smaller than 999 is 995 = 199*5 and the largest multiple of 7 just smaller than 999 is 994 = 142*7

So we have 199 numbers divisible by 5 and 142 numbers divisible by 7. But here we have counted the numbers divisible by both 5 and 7 twice. The largest multiple of 35 less than 999 is 980 = 35*28

So there are 142 + 199 - 28 = 313 numbers divisible by 5 or 7 in the given set of numbers from 0 to 999.

The other numbers are not divisible by either 5 or 7. There are 1000 - 313 = 687 such numbers.