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jmc

prealgebra intermediate

Problem

How many integers between 1 and 200 are multiples of both 3 and 5 but not of either 4 or 7?
Solution
Integers that are multiples of both 3 and 5 must be multiples of 15. We can start by listing the multiples of 15 between 1 and 200: Checking only the even numbers, we can eliminate those that are multiples of 4, leaving us with: Finally, we need to eliminate any remaining multiples of 7. The only multiples of 7 we need to be concerned with are those ending in 5 or 0. The only number on the list that is a multiple of 7 is 105. Our final list is: This leaves us with integers.
Final answer
9