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

Question

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

(1) t^2 – 3 = 6
(2) t^3 = −27

ENGRTOMBA2018 · Accepted Answer

x=2t, y=t/3, x^2 – y^2 = ?

Per statement 1, t^2=9 ---> t= 3 or -3, after substituting both these values, you will get x^2 – y^2 = 35. Sufficient.

Per statement 2, t^3=-27 ---> t=-3, 1 value and hence you will get a unique value of x^2 – y^2. Sufficient

D is the correct choice.

avigutman · Answer

Video solution from Quant Reasoning: Subscribe for more: https://www.youtube.com/QuantReasoning? ... irmation=1 https://www.youtube.com/watch?v=mYnQx75Vj64

cutegirlsimran · Answer

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

(1) t^2 – 3 = 6
(2) t^3 = −27

Sol. x^2 = 4t^2 and y^2 = t^2/9
1) t^2 = 9 so 4t^2 - t^2/9 so 36-1 = 35 
2) t^3 = −27 so t = -3 and t^2=9 so 4t^2 - t^2/9 so 36-1 = 35

D Both Sufficient

GMATinsight · Answer

Given : x = 2t and y = t/3

Question  : x^2 – y^2=(x+y)*(x-y) = ?

Statement 1 : t^2 – 3 = 6 
i.e. t^2 = 9
i.e. t =  + 3
i.e. y = + 1 respectively for respective values of t= + 3 
i.e. x = + 6 respectively for respective values of t= + 3 
i.e. x^2 – y^2 = ( + 6)^2 - ( + 1)^2 = 36-1 = 35
SUFFICIENT

Statement 2 : t^3 = −27 
i.e. i.e. t = -3
i.e. y =-1 respectively for respective values of t= + 3 
i.e. x =-6 respectively for respective values of t= + 3 
i.e. x^2 – y^2 = (-6)^2 - (-1)^2 = 36-1 = 35
SUFFICIENT

Answer: Option D

ThisandThat · Answer

If the question prompt wanted (x^3 - y^3) or (x - y) rather than (X^2 - y^2)

then statement 1 would not be sufficient, correct?

Bunuel · Answer

Yes. In this case the answer would be B.

EMPOWERgmatRichC · Answer

Hi All,

Certain DS questions are really just a 'test' of your 'thoroughness', so it's important to do all of the necessary work (on the pad; NOT 'in your head') to prove what the correct answer is. Without having that 'proof', you might inadvertently choose the wrong answer (and miss out on some easy points on Test Day).

We're told that X = 2T and Y = T/3. We're asked for the value of X^2 - Y^2

1) T^2 - 3 = 6.

With the equation in Fact 1, we can determine that T has 2 values... 
T^2 - 3 = 6 
T^2 = 9 
T = +3 or -3 
Many Test Takers would assume that these two values would lead to two different answers to the question (and assume that Fact 1 was insufficient).... but where is your PROOF that it's insufficient...?

IF.... 
T = 3, X=6, Y=1, then the answer to the question is 6^2 - 1^2 = 35 
IF.... 
T = -3, X= -6, Y= -1, then the answer to the question is (-6)^2 - (-1)^2 = 35 
It turns out that both values of T lead to the SAME answer - and the answer to the question is ALWAYS 35. 
Fact 1 is SUFFICIENT

2) t^3 = -27

The equation in Fact 2 has just one solution: -3. With the work that we did in Fact 1, we know that there is only one answer to the question (35). 
Fact 2 is SUFFICIENT

Final Answer:  D

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

ShankSouljaBoi · Answer

Ok. Was just wondering. Some irrational's irrational power can equal -27. In this case t may not be -3

Please guide.

EMPOWERgmatRichC · Answer

Hi ShankSouljaBoi,

The information in Fact 1 and Fact 2 defines specific 'powers' (a square and a cube), so there's no possibility of an 'irrational power.'

Assuming that you are focusing on Fact 2, we know that there is a CUBED number that equals - 27. By definition, that number MUST be NEGATIVE...

(positive)^3 = positive
(0)^3 = 0
(negative)^3 = negative

In addition, increasing or decreasing the value of the negative will change the value of the cubed term...

(-2)^3 = -8
(-3)^3 = -27
(-4)^3 = -64
Etc.

Thus, even if you are changing the number in really small increments (for example -3 vs -2.999 or -3.1), the end cubed value will change (meaning that there's ONLLY ONE way to get to a -27 result.... when we use -3).

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

GMATinsight · Answer

Answer: Option D

Video solution by  GMATinsight

https://www.youtube.com/watch?v=FywvQVHyKGY

Anisha1637 · Answer

To make the solution easy lets solve the equation in the question first:
putting the values of x and y in the equation we will get:
x^2-y^2= (35t^2)/9

Statement 1 : SUFFICIENT as it gives the value for t which is enough to find the value for x^2-y^2
Statement 2 : SUFFICIENT as it gives the value for t which is enough to find the value for x^2-y^2

therefore, D is the answer

GK002 · Answer

I had put down statement (1) as insufficient because, given t = +/- 3, I had possible values of X as +/- 6 and for Y +/- 1. But when I plug this different values in the equation that we are trying to prove (x+y)(x-y), I got different answers. Sometimes I would get 35, other times I would get -35. Therefore I had selected (1) as sufficient.

For example: 
Y = 1 or -1
X = 6 or -6

Test into equation (x+y)(x-y) to make sure we get the same outcomes.

Test 1: X = 6, Y = 1
(7)(5) = 35

Test 2: X = 6, Y = -1
(5)(7) = 35

Test 3: X = -6, Y = -1
(-7)(-5) = 35

Test 4: X = -6, Y = 1
(-5)(-7) = 35

Oh, wait.... nvm - they all result in 35 - must've been a calculation error... Lol!

ScottTargetTestPrep · Answer

Solution:

We need to determine the value of x^2 - y^2 given that x = 2t and y = t/3. Substituting 2t for x and t/3 for y, we have:

(2t)^2 - (t/3)^2 = 4t^2 - t^2/9 = 35t^2 / 9

Therefore, if we can determine the value of t, we can determine the value of x^2 - y^2 since it’s equal to 35t^2 / 9.

Statement One Alone:

Solving the equation, we have:

t^2 = 9

t = ±√9

t = ±3

Although the value of t is not unique (it can be either 3 or -3), we see that t^2 = 9, regardless of whether t is 3 or -3. Thus, the value of x^2 - y^2 is 35(9) / 9 = 35. Statement one alone is sufficient.

Statement Two Alone:

Solving the equation, we have:

t^3 = -27

t = ∛(-27)

t = -3

Since t = -3, the value of x^2 - y^2 is  /9 = 35(9)/35 = 35. Statement two alone is sufficient.

Answer: D

Anisha1637 · Answer

answer is D
4t^2- t^2/9
 /9
35t^2/9

Now using st 1 and st 2 individually w can find the value

bumpbot · Answer

Automated notice from GMAT Club BumpBot: 

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

 This post was generated automatically.

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

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Data Sufficiency (DS) Questions

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

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards