Hi all,

These types of DS questions can be approached with a mix of Algebra and TESTing VALUES.

We're told that a team played X games and won Y of those games (there were NO ties). We're asked for the value of Y.

Fact 1: If the team lost 2 more games, then it would have won 20% of its games.

Algebraically, you can set up the following equation:

Y - 2 = .2X

This equation does not help you to determine the value of Y.

From a practical standpoint, you can also TEST VALUES:

IF...

X = 5 games

Y = 3 wins

Y-2 = 1 win

1/5 = 20% and the answer to the question is 3.

IF....

X = 10 games

Y = 4 wins

Y-2 = 2 wins

2/10 = 20% and the answer to the question is 4

Fact 1 is INSUFFICIENT

Fact 2: If the team won 3 more games, then it would have lost 30% of its games (meaning the team would have WON 70% of its games

Again, we can use algebra:

Y + 3 = .7X

But we have the same problem we had in Fact 1 - the equation does not help you to determine the value of Y.

Here's the proof by TESTing VALUES:

IF....

X = 10 games

Y = 4 wins

Y+3 = 7 wins

7/10 = 70% and the answer to the question is 4.

IF....

X = 20 games

Y = 11 wins

Y+3 = 14 wins

14/20 = 70% and the answer to the question is 11

Fact 2 is INSUFFICIENT

Combined, we know:

Y - 2 = .2X

Y + 3 = .7X

Here, we have a "system" of equations - with 2 variables and 2 unique equations, we CAN solve and get the value of Y.

Combined, SUFFICIENT

Final Answer:

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

Rich

_________________

# Rich Cohen

Co-Founder & GMAT Assassin

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