If x = 2t and y = t/3, what is the value of x^2 – y^2

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Last Updated on May 10, 2023

GMAT OFFICIAL GUIDE DS

Solution:

Since x = 2t and y = t/3, by substitution, we have

x^2 – y^2

(2t)^2 – (t/3)^2

4t^2 – t^2/9

(36t^2)/9 – t^2/9

(35t^2)/9

So if we know the value of t or t^2, then we can determine the value of (35t^2)/9.

Statement One Alone:

t^2 – 3 = 6

Adding 3 to both sides of the equation, we have t^2 = 9.

Since t^2 = 9, then (35t^2)/9 = (35(9))/9 = 35.

Statement one alone is sufficient. We can eliminate answer choices B, C and E.

Statement Two Alone:

t^3 = −27

Taking the cube root of both sides of the equation, we have t = -3. Since we know t = -3, then

(35t^2)/9 = (35(-3)^2)/9 = (35(9))/9 = 35.

Statement two alone is also sufficient to answer the question.

Answer: D

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