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If x/y = 3/z, then 9y² =

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Math Expert
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If x/y = 3/z, then 9y² =  [#permalink]

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New post 30 Dec 2014, 06:43
1
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

93% (00:42) correct 8% (01:03) wrong based on 160 sessions

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Re: If x/y = 3/z, then 9y² =  [#permalink]

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New post 30 Dec 2014, 07:01
1
The answer is E.

We can solve the equation for y:

\(\frac{x}{y}=\frac{z}{3}=> y=\frac{xz}{3}\).

We square that fraction and get:
\(y^2=\frac{x^2z^2}{9}=\frac{1}{9}*x^2z^2\)
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Re: If x/y = 3/z, then 9y² =  [#permalink]

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New post 30 Dec 2014, 09:25
3
xz=3y
(xz)^2=(3y)^2
(x^2)(z^2)=9y^2

The answer is C
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Re: If x/y = 3/z, then 9y² =  [#permalink]

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New post 30 Dec 2014, 09:37
Sh.... didn't read the question stem properly... I guess I was too tired already.
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Re: If x/y = 3/z, then 9y² =  [#permalink]

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New post 30 Dec 2014, 19:17
Answer = C. x²z²

\(\frac{x}{y} =\frac{3}{z}\)

\(y = \frac{xz}{3}\)

\(y^2 = \frac{x^2 z^2}{9}\)

\(9y^2 = x^2z^2\)
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Re: If x/y = 3/z, then 9y² =  [#permalink]

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New post 31 Dec 2014, 13:44
Bunuel wrote:

Tough and Tricky questions: Algebra.



If x/y = 3/z, then 9y^2 =

A. x²/9
B. x²z
C. x²z²
D. 3x²
E. (1/9)x²z²

Kudos for a correct solution.


x/y = 3/z

xz = 3y
x²z² = 3y²

Ans C
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Re: If x/y = 3/z, then 9y² =  [#permalink]

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New post 31 Dec 2014, 13:57
1
Answer is C
x/y=3/z
=>y = zx/3
9y^2= 9*z^2x^2/9=z^2x^2

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Re: If x/y = 3/z, then 9y² =  [#permalink]

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New post 01 Jan 2015, 18:10
1
x/y=3/z. y=xz/3.
9y²=9*(x*z/3)^2 =(9x^2 *z^2 )/9=x^2*z^2.

Correct answer C.


Bunuel wrote:

Tough and Tricky questions: Algebra.



If x/y = 3/z, then 9y^2 =

A. x²/9
B. x²z
C. x²z²
D. 3x²
E. (1/9)x²z²

Kudos for a correct solution.
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Posts: 52390
Re: If x/y = 3/z, then 9y² =  [#permalink]

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New post 08 Jan 2015, 08:24
1
Bunuel wrote:

Tough and Tricky questions: Algebra.



If x/y = 3/z, then 9y^2 =

A. x²/9
B. x²z
C. x²z²
D. 3x²
E. (1/9)x²z²

Kudos for a correct solution.


OFFICIAL SOLUTION:

(C) This question is most easily solved by isolating y in the equation and substituting into the expression 9y²:
x/y = 3/z
x = 3y/z
3y = xz
y = xz/3.

If we substitute xz/3 into the expression for y, we get:
9(xz/3)² = 9(x²z²/9) = x²z².

The correct answer is choice (C).
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Re: If x/y = 3/z, then 9y² =  [#permalink]

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New post 28 Apr 2017, 09:31
Bunuel wrote:

Tough and Tricky questions: Algebra.



If x/y = 3/z, then 9y^2 =

A. x²/9
B. x²z
C. x²z²
D. 3x²
E. (1/9)x²z²

Kudos for a correct solution.



The soution

(x/y) = 3/z
3y = x*z
9y^2 = x^2 * z ^2

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Re: If x/y = 3/z, then 9y² =  [#permalink]

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New post 16 Dec 2018, 15:39
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Re: If x/y = 3/z, then 9y² = &nbs [#permalink] 16 Dec 2018, 15:39
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