So I am doing some practice problems and I was wondering if someone can clarify what the question is asking.

The question:

a) How many integers between 1 and 400 (inclusive) are divisible by at least one of 4,5 and 20?

b) How many integers between 1 and 400 (inclusive) are divisible by just one of 4,5 and 20?

a) I am thinking the question is asking divisible by 4 and 5 and 20

b) I am thinking the question is asking divisible by one of 4 or 5 or 20

Can someone clarify for 'a' and 'b'?

Thanks.