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If b#1, what is the value of a in terms of b if ab/(a-b)=1 ?

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If b#1, what is the value of a in terms of b if ab/(a-b)=1 ? [#permalink] New post 23 Mar 2012, 07:37
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If b\neq{1}, what is the value of a in terms of b if ab/(a-b)=1?

A. \frac{b}{1-b}

B. \frac{b-1}{b}

C. \frac{b}{b+1}

D. \frac{b+1}{b}

E. \frac{1-b}{b}

The answer is b/1-b but I'm not sure how they got it.
[Reveal] Spoiler: OA

Last edited by Bunuel on 23 Mar 2012, 07:58, edited 2 times in total.
Edited the question and added the OA
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Re: isolating a variable [#permalink] New post 23 Mar 2012, 07:55
Expert's post
Jakevmi80 wrote:
If b is not = 1 and ab/a-b =1, what is the value of a in terms of b?

The answer is b/1-b but I'm not sure how they got it.


Question should read:
If b\neq{1}, what is the value of a in terms of b if \frac{ab}{a-b}=1?

A. \frac{b}{1-b}

B. \frac{b-1}{b}

C. \frac{b}{b+1}

D. \frac{b+1}{b}

E. \frac{1-b}{b}

\frac{ab}{a-b}=1 --> cross-multiply: ab=a-b --> rearrange: b=a-ab --> factor out a: b=a(1-b) --> a=\frac{b}{1-b}.

Answer: A.

P.S Please post answer choices with PS questions.
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Re: isolating a variable   [#permalink] 23 Mar 2012, 07:55
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If b#1, what is the value of a in terms of b if ab/(a-b)=1 ?

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