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# Is ab = 1 ? (1) aba = a (2) bab = b

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Manager
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Is ab = 1 ? (1) aba = a (2) bab = b [#permalink]

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22 Aug 2003, 11:01
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19. Is ab = 1 ?
(1) aba = a
(2) bab = b

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Manager
Joined: 02 Jul 2003
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22 Aug 2003, 11:22
does the question preface with a and b are not equal to zero.

If not than E

because if a and b are zero the solution works and if you use a number and it's inverse the solution works.

Rich

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Manager
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22 Aug 2003, 11:27
Ignore that last post-it's been a long week. Hopefully this works.

D

1 reduces to 1/a=b

2 reduces to 1/b=a

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Manager
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22 Aug 2003, 12:03
But the answer is E and i Cant figure out why and how?? please explian

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GMAT Instructor
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22 Aug 2003, 15:31
aps_can wrote:
But the answer is E and i Cant figure out why and how?? please explian

When you divide both sides of an equation by a variable, you have to exclude the possibility that the variable is equal to zero.

In both 1 and 2, you divide by a variable. This means that the results hold true PROVIDED a and b are not zero. However, in both 1 and 2 would be true if a and b were zero, but ab is equal to zero, not 1. Hence, E is the answer.
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AkamaiBrah
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993

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Manager
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22 Aug 2003, 15:45
boss its not clear, please explain this"However, in both 1 and 2 would be true if a and b were zero, but ab is equal to zero, not 1. Hence, E is the answer"
incase we are dividing both sides by a or b then and b are not 0 also ab is not 0? am i right.
Sorry boss but this is my weak area. i loved doing ur C&P problems, it really helped me clear my fundamentals.

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GMAT Instructor
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22 Aug 2003, 16:06
aps_can wrote:
boss its not clear, please explain this"However, in both 1 and 2 would be true if a and b were zero, but ab is equal to zero, not 1. Hence, E is the answer"
incase we are dividing both sides by a or b then and b are not 0 also ab is not 0? am i right.
Sorry boss but this is my weak area. i loved doing ur C&P problems, it really helped me clear my fundamentals.

The question is: Is ab = 1?

If a and b are not zero and 1 and 2 are true, then ab = 1
If a and b are zero, 1 and 2 are still true, but ab = 0.

Hence, we cannot determine whether ab = 1 simple based on whether 1 and 2 together are true.
_________________

Best,

AkamaiBrah
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993

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Manager
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22 Aug 2003, 16:25
Super!
I must say u've got excellent explanation skills.

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Thanks   [#permalink] 22 Aug 2003, 16:25
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