Practice GMAT Data Sufficiency Question

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How many computers did Michael, a salesman for the computer company Digital Electronics Labs, sell this past year that had more than 4GB of RAM and the Microsoft Windows Vista operating system? (Michael sold no computers with exactly 4GB of RAM)

40% of the 200 total computers that Michael sold had Vista and less than 4GB of RAM; these computers represent 80% of the total computers that Michael sold with Vista.
50% of the 200 total computers that Michael sold had Vista; Of the computers that Michael sold without Vista, half had more than 4GB of ram while the other half had less than 4GB of RAM.

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: A

Evaluate Statement (1) alone.
1. 40% of 200 is 80, so Michael sold 80 computers with Vista and less than 4GB of RAM.
2. These 80 computers represent 80% of the total computers Michael sold with Vista, so Michael sold a total of 100(=80/80%) computers with Vista.
3. Vista_total = Vista_<4GB + Vista_>4GB
  100 = 80 + Vista_>4GB
  Vista_>4GB = 20
4. Statement (1) alone is SUFFICIENT.
5. Note: At this point, you should not continue making calculations since you have determined sufficiency. However, to be complete, we included additional information you can deduce:
  Vista_Total + NoVista_Total = Total
  100 + NoVista_Total = 200
  NoVista_Total = 100 and Michael sold a total of 100 computers without Vista.
  
  Vista No Vista Total
  
  > 4GB RAM 20
  
  < 4GB RAM 80
  
  Total 100 100 200
Evaluate Statement (2) alone.
1. "50% of the 200 total computers that Michael sold had Vista" means that 100 computers had Vista. Consequently, 100 computers Michael sold did not have Vista.
2. "Of the computers that Michael sold without Vista, half had more than 4GB of RAM while the other half had less than 4GB of RAM" means that one-half of the 100 computers without Vista (i.e., 50) had more than 4GB of RAM while the other half (i.e., 50) had less than 4GB of RAM.
3. Put this information into a table:
  
  Vista No Vista Total
  
  > 4GB RAM ?= 50
  
  < 4GB RAM 50
  
  Total 100 100 200
4. We cannot determine the number of computers sold both with Vista and more than 4GB of RAM, so Statement (2) is NOT SUFFICIENT.
5. Statement (2) alone is NOT SUFFICIENT.
Since Statement (1) alone is SUFFICIENT and Statement (2) alone is NOT SUFFICIENT, answer A is correct.

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