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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]

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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]

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New post 23 Mar 2012, 07:55
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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