Data Sufficiency

Hi dddanny2006,

The DS question is built around a "system" of equations. By knowing the rules of "system math", you can sometimes avoid the calculations and still come up with the correct answer.

**Based on what you wrote below the question, in the original question, does Fact 2 state it was 20% fewer SMALL postcards sold? If so, then this becomes even easier to solve.**

Based on the prompt, we have this equation (I've combined the two equations that we would form into one big equation and I've used the variables that you used):

950(2x) + S(x) = 2400

Here we have 2 variables, but only one equation. Since the prompt asks us to solve for S, we need one more unique equation that includes x, S or both.

Fact 1 tells us that 2x = 2, so with the value of x, we can plug in and solve for S.
We'd get:
950(2) + S(1) = 2400
S = 500
Fact 1 is SUFFICIENT

Fact 2 would give us the equation that you wrote:
950(2x) + .8S(x) = 2300

Since the 20% drop = $100 of lost revenue, we have this:
.2S(x) = 100
S(x) = 500

Now, plug THAT back into the original equation. You'd have:
950(2x) + 500 = 2400

Solve for x. You'll get x = 1, which you can plug in and get S = 500
Fact 2 is SUFFICIENT

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

ganeshrkamath wrote:The statement just says "20% fewer postcards". This means it's the total number of cards, right?

Right.

So, the question was probably transcribed incorrectly at some point (perhaps in the original source... yikes!)
It's most likely supposed to say "small" in front of "postcards" in that statement.