Data Sufficiency

[Math Revolution GMAT math practice question]

If m and n are positive integers, is 3^{4m+2}+n divisible by 5?

1) m=3
2) n=1

=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.

The units digits of 3^k have period 4 as they form the cycle 3 -> 9 -> 7 -> 1.
3^{4m+2} has 9 as its units digit if 3^{4m+2} has units digit 9, regardless of the value of m.
Thus, the divisibility of 3^{4m+2}+n by 5 relies on the variable n only.

Therefore, the correct answer is B.
Answer: B