Practice GMAT Data Sufficiency Question

Chef Martha is preparing a pie for a friend's birthday. How much more of substance X does she need than substance Y?

Martha needs 10 cups of substance X
Martha needs the substances W, X, Y, and Z in the ratio: 15:5:2:1 and she needs 4 cups of substance Y

A)	Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B)	Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C)	BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D)	EACH statement ALONE is sufficient.
E)	Statement (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data are needed.

Correct Answer: B

The phrase "how much more of substance X does she need than substance Y" can be translated into algebra as: X - Y
Evaluate Statement (1) alone.
1. Although X = 10, there is no information about Y. Consequently, we cannot determine the value of X - Y
2. Statement (1) is NOT SUFFICIENT.
Evaluate Statement (2) alone.
1. Y = 4 and the ratio of X:Y = 5:2. Consequently, X = 10 and X - Y = 10 - 4 = 6
2. Statement (2) is SUFFICIENT.
Since Statement (1) alone is NOT SUFFICIENT but Statement (2) alone is SUFFICIENT, answer B is correct.