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Advanced Gmat quant - chapter 4, question 9 - CONFUSING

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ozlen_bilen
 Post subject: Advanced Gmat quant - chapter 4, question 9 - CONFUSING
 Post Posted: Wed Nov 09, 2011 4:53 am 
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Students


Posts: 1
Hi,

I do not understand the explanation given in your book for the following data sufficiency question.

If a ≠ 0, is 1/a > a/b4+3
(1) a2 = b2
(2) a2 = b4

In the book it is said that the 1st answer choice is sufficient because b2 must be positive, so a is positive. I do not understand this part, why a should be positive and not negative.
Also, in the 2nd answer choice, this is the case; a2 = b4 can be true with positive or negative values of a.
So I do not understand why in first choice a must be absolutely positIve while it can be negative in the 2nd one.

Thank you for your clarification.
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StaceyKoprince
 Post subject: Re: Advanced Gmat quant - chapter 4, question 9 - CONFUSING
 Post Posted: Tue Nov 15, 2011 12:13 am 
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ManhattanGMAT Staff


Posts: 6064
Location: San Francisco
It's helpful if you can give us the page number, too - just makes it easier to look up the problem. Thanks!

When typing things with exponents, use this symbol to indicate the exponent: ^

So the problem reads:
If a ≠ 0, is 1/a > a/[(b^4)+3]
(1) a^2 = b^2
(2) a^2 = b^4

Okay, now here's the answer to your question. There's a typo in the problem! The first statement is supposed to say "a = b^2" NOT "a^2 = b^2."

Does that make more sense now? :)

You can find the full error list here:
http://www.manhattangmat.com/errata-adv-quant-4th.cfm

And sorry for the error! It was probably driving you crazy.

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Stacey Koprince
Instructor
Director of Online Community
ManhattanGMAT
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