GMAT Tip of the Week: Data Sufficiency and The Imitation Game

GMAT Tip of the WeekWith Oscar weekend upon us, it’s only fitting that this week’s GMAT Tip comes courtesy of Alan Turing. Of course the brilliant math mind featured in Best Picture nominee The Imitation Game would crush GMAT Data Sufficiency. But the mere title of the film provides a GMAT tip that can help bring Data Sufficiency success to even us mere mortals who can’t quite use math to save Britain from peril. How can you use The Imitation Game to succeed on Data Sufficiency?

When you’re asked a Yes/No Data Sufficiency question that asks whether an algebraic relationship is true, play The Imitation Game. Which means: if you can get one of the statements to directly imitate the question, you can definitively get the answer “yes” and prove that it’s sufficient.

Consider a few examples of questions that make for great Imitation Game candidates:

Is x – y > a – b?

(1) x + b > a + y

Here you can try to imitate the question with the statement. You want the statement to look more like the question, where x and y are paired together on the left and a and b are paired together on the right. so subtract y from both sides (to get it from the right to the left) and subtract b from both sides (to move it to the right), and the statement becomes:

x – y > a – b

Which directly answers the question “yes” – the question asks if the relationship is true, and by using the statement to imitate the question you can get the statement to directly answer it.

If the product abc does not equal 0, does a/b = c?

(1) bc = a

Here you can again use the statement to imitate the question, dividing both sides by b to get c on its own (which you’re allowed to do since no values are 0), and you have your answer:

c = a/b

Sometimes you’ll be able to imitate the question to get a definite “no” answer, which is still sufficient:

Is x – y > a – b?

(1) a > x and y > b

Here you can combine the inequalities to get them all in to one inequality. By adding the inequalities together (which you can do since the signs point in the same direction), you have:

a + y > x + b

And then you want to imitate the question, which has a and b on one side and x and y on the other. So subtract y and b from both sides to get:

a – b > x – y

Which is the opposite of the question, and therefore says “no, x – y is not greater than a – b” providing you with sufficient information.

The real lesson here? When you’re being asked a yes/no question with lots of algebra, it pays to play The Imitation Game. See if you can get the statement to imitate the question, and you’ll often find that it directly answers the question.

But be careful! As the second example showed you, you need to be careful when diving into algebra that you don’t:

*Divide by a variable that could be 0
*Multiply or divide by a variable in an inequality if you don’t know the sign

Keep those two caveats in mind and you can imitate math legend Alan Turing while you play the Data Sufficiency Imitation Game. And the winner is…you.