This is a question in Kenneth Rosen's Discrete Mathematics textbook 6th edition. I haven't had trouble with any other counting problems regarding "how many numbers in range [x,y] have divisibility property Z?" My issue is I have no idea what Rosen is asking for, i.e. I don't understand the question because I don't know what he wants me to compute.
Therefore this is not a duplicate of this question (1) https://math.stackexchange.com/questions/588160/how-many-positive-integers-less-than-1000-are-divisible, since while the answer is given, it doesn't explain the language of the question and what is being computed. I have no idea why the number of integers divisible by 7 or 11 minus the number of integer divisible by 77 (11 and 7) is the answer to this question. Both of these values I've already computed correctly (in separate questions).
In context: 20. How many positive integers less than 1000 e) are divisible by exactly one of 7 and 11?
Thus my question is: what/which numbers am I supposed to count/compute?