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For any numbers a and b, ab= a + b - ab. If ab=0, which of the following CANNOT be a value of b?

A. 2 B. 1 C. 0 D. -1 E. -3/2

Some function (#) is defined for all numbers \(a\) and \(b\) as \(a#b= a + b - ab\).

Now, since given that \(a#b=0\), then \(a + b - ab=0\) --> \(a=\frac{b}{b-1}\) --> if \(b=1\) then the given expression is undefined so \(b\) cannot equal to 1.

Or: \(a + b - ab=0\) --> \((a-1)(1-b)+1=0\) --> \((a-1)(1-b)=-1\). If \(b=1\), then \((a-1)(1-b)=0\) not -1, so \(b\) cannot equal to 1.

Re: For any numbers a and b, ab= a + b - ab. If ab=0, which of [#permalink]

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06 Jul 2012, 00:55

Can someone pls edit the question.? i was wondering where i was going wrong thinking. question was ab=a+b-ab => 2ab=a+b. and then saw bunuel's reply then understood what the question was!
_________________

Re: For any numbers a and b, ab= a + b - ab. If ab=0, which of [#permalink]

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25 Jul 2012, 01:40

asax wrote:

Can someone pls edit the question.? i was wondering where i was going wrong thinking. question was ab=a+b-ab => 2ab=a+b. and then saw bunuel's reply then understood what the question was!

Even I got it wrong...
_________________

I've failed over and over and over again in my life and that is why I succeed--Michael Jordan Kudos drives a person to better himself every single time. So Pls give it generously Wont give up till i hit a 700+

Re: For any numbers a and b, ab= a + b - ab. If ab=0, which of [#permalink]

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11 Apr 2013, 04:59

asax wrote:

Can someone pls edit the question.? i was wondering where i was going wrong thinking. question was ab=a+b-ab => 2ab=a+b. and then saw bunuel's reply then understood what the question was!

Can someone pls edit the question.? i was wondering where i was going wrong thinking. question was ab=a+b-ab => 2ab=a+b. and then saw bunuel's reply then understood what the question was!

Re: For any numbers a and b, a#b=a + b - ab. If a#b=0, which of [#permalink]

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11 Apr 2013, 05:15

Stiv wrote:

For any numbers a and b, a#b=a + b - ab. If a#b=0, which of the following CANNOT be a value of b?

A. 2 B. 1 C. 0 D. -1 E. -3/2

------------------------------------------ for me the fastest way must be the use of answer choices to find the value of a if a will be an integer after putting the value of of b as given in the answer choices then the answer will be correct with no cumbersome calculations & its fast too ....!! _________________

If you don’t make mistakes, you’re not working hard. And Now that’s a Huge mistake.

Re: For any numbers a and b, a#b=a + b - ab. If a#b=0, which of [#permalink]

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16 Jul 2014, 21:40

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
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