GMAT Data Sufficiency Explanation

6. Yesterday it rained in Baronia. Did it rain in Dukia?

1. Whenever it rains in Dukia, it also rains in Baronia.
2. If it does not rain in Dukia, it does not rain in Baronia.

A. statement 1 alone is sufficient, but statement 2 alone is not sufficient to answer the question
B. statement 2 alone is sufficient, but statement 1 alone is not sufficient to answer the question
C. both statements taken together are sufficient to answer the question, but neither statement alone is sufficient
D. each statement alone is sufficient
E. statements 1 and 2 together are not sufficient, and additional data is needed to answer the question

Correct Answer: B

Explanation:

In Dukia it could either rain or not rain. If it rains in Dukia it will also rain in Baronia, but that leaves open the possibility that it could rain in Baronia without it raining in Dukia, and hence statement (1) is not enough to be sure. Now (forgetting statement 1), if it does not rain in Dukia it will not rain in Baronia, but we know it rained in Baronia, so it could not have been fine in Dukia! So we have answered the question using only statement (2).