Question: how many numbers between 1 and 100 divisible by 7?
Answer: There are 10 numbers divisible by 10 between 1 and 100, and 14 numbers divisible by 7 between 1 and 100. So there are 10 + 14 = 24, so 24 numbers divisible by one or the other, but this also includes every number which is divisible by both 7 and 10 twice.