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smc

algebra senior

Problem

The sum of terms of an arithmetic progression is , and the common difference is . If the first term is an integer, and , then the number of possible values for is:
(A)
(B)
(C)
(D)
Solution
Let the progression start at , have common difference , and end at . The average term is , or . Since the number of terms is , and the sum of the terms is , we have: Since is a positive integer, it must be a factor of . This means are the only possibilities. We are given , leaving the other five factors. We now must check if is an integer. We have . If is a factor of , then will be an integer. Adding wil keep it an integer. Thus, there are possible values for , which is answer .
Final answer
D