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If xy = 4, what is the value of xy(x – y) ?

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V
Joined: 02 Sep 2009
Posts: 41873

Kudos [?]: 128601 [0], given: 12180

If xy = 4, what is the value of xy(x – y) ? [#permalink]

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New post 19 Sep 2017, 01:30
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  45% (medium)

Question Stats:

77% (01:38) correct 23% (01:03) wrong based on 31 sessions

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Kudos [?]: 128601 [0], given: 12180

Intern
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B
Joined: 17 Oct 2016
Posts: 28

Kudos [?]: 3 [0], given: 59

Location: India
Concentration: Operations, Strategy
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Re: If xy = 4, what is the value of xy(x – y) ? [#permalink]

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New post 19 Sep 2017, 02:09
A

Substitute xy value in x^2*y=16. It will give us x=4&y=1

B doesn't give any specific values.

So option A


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Re: If xy = 4, what is the value of xy(x – y) ? [#permalink]

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New post 19 Sep 2017, 02:27
If xy = 4
Find: xy(x – y)

(1) x^2*y = 16
=> x * xy = 16 => x=4
=> as xy=4 => y =1
so xy(x-y) = 4(4-1) = 4*3 = 12
Sufficient

(2) x + y = 5
xy=4 => \(x=\frac{4}{y}\)
\(\frac{4}{y}+ y= 16\) => \(y^2-5y+4 = 0\) => y=1 or 4
as xy=4 => x=4 or 1.
As we have 2 values of x and y we get 2 values for xy(x – y)
Insufficient

Answer: A

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Re: If xy = 4, what is the value of xy(x – y) ? [#permalink]

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New post 23 Sep 2017, 22:24
Bunuel wrote:
If xy = 4, what is the value of xy(x – y) ?

(1) x^2*y = 16
(2) x + y = 5


hi

statement 1 states that x is equal to 4, and y is equal to 1, hence sufficient..

statement 2, however, provides 2 options
either
x = 1
y = 4
or
x = 4
y = 1
not sufficient ...

thanks ..

Kudos [?]: 13 [0], given: 400

Re: If xy = 4, what is the value of xy(x – y) ?   [#permalink] 23 Sep 2017, 22:24
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