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Manager  Joined: 26 Oct 2010
Posts: 59
If wx = y, then what is the value of xy?  [#permalink]

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Difficulty:   35% (medium)

Question Stats: 63% (01:04) correct 37% (01:38) wrong based on 269 sessions

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If wx = y, then what is the value of xy?

(1) w*x^2 = 16
(2) y = 4
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Math Expert V
Joined: 02 Sep 2009
Posts: 55271
Re: If wx = y, then what is the value of xy?  [#permalink]

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jonblazon wrote:
Could someone please help me with this one?

if wx=y, then what is the value of xy?

1) wx^2= 16 (w times x squared)

2) y= 4

thanks!

If wx=y, then what is the value of xy?

(1) wx^2 = 16 --> $$x*(wx)=16$$ --> as given that $$wx=y$$ then $$x*y=16$$. Sufficient.

(2) y = 4 --> clearly insufficient: question becomes $$4x=?$$, and all we know is that $$wx=4$$.

Answer: A.
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Manager  Joined: 26 Oct 2010
Posts: 59
Re: If wx = y, then what is the value of xy?  [#permalink]

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super thanks! should have seen it was that easy
Manager  Status: what we want to do, do it as soon as possible
Joined: 24 May 2010
Posts: 72
Location: Vietnam
WE 1: 5.0
Re: If wx = y, then what is the value of xy?  [#permalink]

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+1 for Jonblazon for good question. I got C for uncareful observation
+1 for Bunuel: you are amazing
Thanks once again for your good question, at least to me. _________________
Consider giving me kudos if you find my explanations helpful so i can learn how to express ideas to people more understandable.
Intern  Joined: 05 Mar 2014
Posts: 5
Re: If wx = y, then what is the value of xy?  [#permalink]

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Usually when I have a DS question I try to come up with the equations and respective variables that I need. Then I count the equations and unknowns and if I have more unknowns than I have equations I know it's not sufficient.
Here I'm not sure if the approach is feasible, but I'd like to give it a try. Please give me your opinions on the approach:

1. We have the equation wx = y and we need to find xy = ?. In order to do so we don't need to know x or y, but only w (if we have w, we're able to find xy, as wx = y is given). Therefor w is our only unknown.

(1) we get wx^2=16. As we don't need to handle x as an unknown (see above) we can count what we have: here it's 1 unknown (w) and 1 equation => sufficient
(2) we get y=4. y isn't an unknown in this approach, so when we count: 1 unknown (w) and 0 equations => not sufficient

So it's A.
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Re: If wx = y, then what is the value of xy?  [#permalink]

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1
i mistakenly took it as (wx)^2
and got wx = +-4 which is insufficient; 2 is as well insufficient..
eh..can't say it's not my fault, but the topic starter should have put the math code here :D
Math Expert V
Joined: 02 Sep 2009
Posts: 55271
Re: If wx = y, then what is the value of xy?  [#permalink]

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mvictor wrote:
i mistakenly took it as (wx)^2
and got wx = +-4 which is insufficient; 2 is as well insufficient..
eh..can't say it's not my fault, but the topic starter should have put the math code here :D

The point is that wx^2 mathematically can only mean w*x^2. If it were (wx)^2 it would be written that way. Still edited to avoid confusion.
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Board of Directors P
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Re: If wx = y, then what is the value of xy?  [#permalink]

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Bunuel wrote:
mvictor wrote:
i mistakenly took it as (wx)^2
and got wx = +-4 which is insufficient; 2 is as well insufficient..
eh..can't say it's not my fault, but the topic starter should have put the math code here :D

The point is that wx^2 mathematically can only mean w*x^2. If it were (wx)^2 it would be written that way. Still edited to avoid confusion.

Thanks bunuel, but it was not needed. I admit that it was my mistake, and that I should have been more attentive. Indeed wx^2 represents w*x^2

I was speaking about $$wx^2$$ rewriting in this format Intern  B
Joined: 19 Jun 2017
Posts: 48
GMAT 1: 660 Q39 V40 GMAT 2: 700 Q45 V41 Re: If wx = y, then what is the value of xy?  [#permalink]

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I'm sorry, I've spent 20 mins trying to puzzle this out but just can't get it.

What if we were to pick numbers?

WX=Y

If W were 1 and X were 4, then Y would be 4.

Using statement 1; WX^2 = 16 would mean 1 x 4^2 = 16

This satisfied the number I'd picked earlier and Y remains 4.

But if I had chosen W as 16 and X as 1, then WX = 16

Using statement one -> 16 x 1^2 = 16

This also satisfied picking W as 16 and X as 1, but now the value of WX is 16 wich means that Y is also 16.

So i get two different possible values for Y: 4 and 16.

What am I doing wrong?
Math Expert V
Joined: 02 Sep 2009
Posts: 55271
Re: If wx = y, then what is the value of xy?  [#permalink]

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calappa1234 wrote:
I'm sorry, I've spent 20 mins trying to puzzle this out but just can't get it.

What if we were to pick numbers?

WX=Y

If W were 1 and X were 4, then Y would be 4.

Using statement 1; WX^2 = 16 would mean 1 x 4^2 = 16

This satisfied the number I'd picked earlier and Y remains 4.

But if I had chosen W as 16 and X as 1, then WX = 16

Using statement one -> 16 x 1^2 = 16

This also satisfied picking W as 16 and X as 1, but now the value of WX is 16 wich means that Y is also 16.

So i get two different possible values for Y: 4 and 16.

What am I doing wrong?

What question are you answering? The question asks: what is the value of xy? In both of your examples xy comes to be 16.
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Intern  B
Joined: 19 Jun 2017
Posts: 48
GMAT 1: 660 Q39 V40 GMAT 2: 700 Q45 V41 Re: If wx = y, then what is the value of xy?  [#permalink]

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Oh my, never mind! I've been trying to read way to deep into this question and have in turn, contorted it into something else entirely in my mind. I see now, how simple it actually is. Sorry for the confusion, and thanks for clearing it up!
Intern  B
Joined: 14 Jul 2017
Posts: 21
Re: If wx = y, then what is the value of xy?  [#permalink]

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If wx = y, then what is the value of xy?

(1) w*x^2 = 16
(2) y = 4

I solved it like this
1) w*x^2 /x^2 = 16/x^2 (divide by x^2 on both side)
w= 16/x^2
Put this in original equation wx = y --> (16/x^2)*x = y -->16/x = y
So, xy = x* (16/x) = 16 Hence, sufficient.

Can we solve it this way aswell??
Retired Moderator P
Joined: 22 Aug 2013
Posts: 1443
Location: India
Re: If wx = y, then what is the value of xy?  [#permalink]

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RashmiT wrote:
If wx = y, then what is the value of xy?

(1) w*x^2 = 16
(2) y = 4

I solved it like this
1) w*x^2 /x^2 = 16/x^2 (divide by x^2 on both side)
w= 16/x^2
Put this in original equation wx = y --> (16/x^2)*x = y -->16/x = y
So, xy = x* (16/x) = 16 Hence, sufficient.

Can we solve it this way aswell??

Hello

Yes, I think we can do it this way as well.
CEO  V
Joined: 12 Sep 2015
Posts: 3727
Location: Canada
Re: If wx = y, then what is the value of xy?  [#permalink]

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Top Contributor
jonblazon wrote:
If wx = y, then what is the value of xy?

(1) w*x^2 = 16
(2) y = 4

Given: wx = y

Target question: What is the value of xy ?

Statement 1: wx²= 16
We can rewrite this as: (wx)(x) = 16
Since wx = y, we can replace wx with y to get: (y)(x) = 16
So, the answer to the target question is xy = 16
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: y = 4
There are several values of w, x and y that satisfy statement 2. Here are two:
Case a: w = 1, x = 4 and y = 4. In this case, the answer to the target question is xy = 16
Case b: w = 2, x = 2 and y = 4. In this case, the answer to the target question is xy = 8
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Answer: A

Cheers,
Brent
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Senior Manager  G
Joined: 25 Feb 2019
Posts: 285
Re: If wx = y, then what is the value of xy?  [#permalink]

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Good question,

just needed presence of mind ...

IMO A

put wx= y in statement 1

we get xy = 16

Posted from my mobile device Re: If wx = y, then what is the value of xy?   [#permalink] 09 Apr 2019, 10:57
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