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number theory intermediate

Problem

Eleanor is making chocolate chip cookies for her friends. If she divides the cookies equally among of her friends, she'll have cookies left over. If she divides the cookies equally among of her friends, she'll have cookie left over. Assuming that Eleanor made fewer than cookies, what is the sum of the possible numbers of cookies that she could have made?
Solution
If Eleanor made cookies, we know from the first requirement that for some integer and from the second requirement we know that for some integer Therefore, If we list the possible values of such that we have The only members of this list divisible by are and and so the possible values of are and , and thus the sum of the possible numbers of cookies is
Final answer
107