Ellen can purchase a certain computer at a local store at th

Hi All,

Certain types of DS questions will appear on Test Day to measure the thoroughness of your thinking. You can see from the statistics above this prompt that almost half of the people who attempted it got it wrong. My guess is that most (if not all) of them COULD have gotten it correct, but they just didn't do enough work to PROVE what the correct answer is.

The prompt tells us about two ways that Ellen could purchase a computer:
1) From a store - for $P + 6% tax
2) From a catalog - for a total price of $Q

We're asked if it will cost Ellen MORE to buy the computer from the store than from the catalog. In real simple terms, it's asking "Is 1.06(P) > Q?" This is a YES/NO question.

Fact 1: Q - P < 50

From this, we don't know if Q or P is bigger, but we can still TEST VALUES to prove the inconsistency....

IF...
Q = 50
P = 1
1.06(1) is NOT > 50. The answer to the question is NO.

IF....
Q = 50
P = 53
1.06(53) IS > 50. The answer to the question is YES.
Fact 1 is INSUFFICIENT.

Fact 2: Q = 1150

This tells us nothing about the value of P, so we cannot figure out the value of 1.06(P).
Fact 2 is INSUFFICIENT

Combined, we know....
Q - P < 50
Q = 1150

At this point, many Test Takers would assume that this was insufficient, without gathering ANY proof. It's always interesting when Quant questions include specific numbers - those numbers were CHOSEN for a reason. They are NOT by accident. So it's interesting that Q = 1150 EXACTLY. Maybe there's a reason....maybe there's a pattern here....

Substituting in the value of Q, we have...

1150 - P < 50
1100 < P

Now this provides a lower limit to what P can be, but we MUST factor in the 6% tax too....

At the 'low end', P = just over $1100. With a 6% tax, (.06)(1100) = $66, so 1.06(P), at the minimum = a little more than 1100 + 66 = $1166. Every other possible price for P is GREATER than this. By extension, EVERY possible value of 1.06(P) is greater than Q.
Combined, SUFFICIENT.

Final Answer:

GMAT assassins aren't born, they're made,
Rich