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algebra senior

Problem

If is a positive integer, then can be a positive integer, if and only if is:
(A)
(B)
(C)
(D)
Solution
Lets begin by noticing that: Therefore, in order for to be a positive integer, must be a non-negative integer. Since the bottom the the fraction is an odd number, we can multiply the top of by 2 without changing whether it is an integer or not. Therefore, in order for to be an integer, must also be an integer. As a result, must be a factor of 65, or . Therefore must be at least 3, and less than or equal to 35. So the answer which best fits these constraints is .
Final answer
B