Data Sufficiency

For Data Sufficiency questions, first ask yourself what you need to know. Here, to find k, you need to know m - n (isolate k in the equation).

Statement 1, viewed in isolation, gives you only n, not m, so it is not sufficient. Thus, the possible answers are B, C, and E.

Statement 2, viewed in isolation, allows you to solve for m - n, so it is sufficient. Thus, the answer is (B).

When (1) is insufficient and (2) is sufficient, there is no need to combine the two statements. You consider them together only if each is insufficient on its own.

Cheers,