Practice GMAT Data Sufficiency Question

n is a positive number; z – 15 is also a positive number; is z/n less than one?

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: D

The value of a fraction is less than one if its numerator is smaller than its denominator. For example, 4/6 is less than one because 4 < 6. So, the question at hand can be simplified to: is z < n?
Evaluate Statement (1) alone.
1. Statement (1) can be re-arranged:
  z - n > 0
  z > n
2. Since z > n, you can definitively answer no to the question: "is z < n?"
3. Statement (1) is SUFFICIENT.
Evaluate Statement (2) alone.
1. Based upon the question, since z-15 is a positive number, the following inequality must hold:
  z - 15 > 0
  z > 15
2. Statement (2) says:
  n < 15
3. Since z > 15 and n < 15, you know that z > n
4. You can definitively answer no to the question: "is z < n?"
5. Statement (2) is SUFFICIENT.
Since Statement (1) alone is SUFFICIENT and Statement (2) alone is SUFFICIENT, answer D is correct.