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16 Jan 2013, 08:57
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If ab = ac is b = 2 ?
(1) c = 1
(2) a is a prime number and c is NOT a prime number
I got this step correct \(a(b-c)=0\) : either \(a=0\) or \(b=c\)
But (1), i selected this one as the answer along with (2)
Not sure why this isn't correct. My understanding says b = 1 because b = c, which is 1.
Not able to understand (1)'s explanation:- \(c=1\) . If \(a=0\) then \(b\) can take any value irrespective of the value of \(c\) . Not sufficient.
Please explain this in detail.
Thanks & Regards
Vinni
(1) c = 1
(2) a is a prime number and c is NOT a prime number
I got this step correct \(a(b-c)=0\) : either \(a=0\) or \(b=c\)
But (1), i selected this one as the answer along with (2)
Not sure why this isn't correct. My understanding says b = 1 because b = c, which is 1.
Not able to understand (1)'s explanation:- \(c=1\) . If \(a=0\) then \(b\) can take any value irrespective of the value of \(c\) . Not sufficient.
Please explain this in detail.
Thanks & Regards
Vinni
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16 Jan 2013, 10:01
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vinnik
OFFICIAL SOLUTION:
If \(ab=ac\) is \(b=2\)?
Notice that we cannot reduce \(ab=ac\) by \(a\) and write \(b=c\), since \(a\) can be zero and division by zero is not allowed. \(ab=ac\) --> \(a(b-c)=0\) --> either \(a=0\) or \(b=c\).
(1) \(c=1\) --> if \(a=0\) then \(b\) can tale any value irrespective of the value of \(c\). Not sufficient.
(2) \(a\) is a prime number and \(c\) is NOT a prime number --> \(a=prime\) means that \(a\neq{0}\), so it must be true that \(b=c\). Now, since also given that \(c\neq{prime}\) then \(b\) is also not equal to a prime number so it cannot equal to a prime number 2. Sufficient.
Answer: B.
Notice that we cannot reduce \(ab=ac\) by \(a\) and write \(b=c\), since \(a\) can be zero and division by zero is not allowed. \(ab=ac\) --> \(a(b-c)=0\) --> either \(a=0\) or \(b=c\).
(1) \(c=1\) --> if \(a=0\) then \(b\) can tale any value irrespective of the value of \(c\). Not sufficient.
(2) \(a\) is a prime number and \(c\) is NOT a prime number --> \(a=prime\) means that \(a\neq{0}\), so it must be true that \(b=c\). Now, since also given that \(c\neq{prime}\) then \(b\) is also not equal to a prime number so it cannot equal to a prime number 2. Sufficient.
Answer: B.
As for your question. We have that either a=0 OR b=c.
Now, if for (1) a=0, then b can take ANY value. Consider a=0, c=1 and b=(any value) --> ab=ac=0.
Hope it's clear.
16 Jan 2013, 10:45
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Bunuel
ab = ac
0 * b = 0 * 1
got it. Thank you.
Regards
Vinni
Archived Topic
Hi there,
Archived GMAT Club Tests question - no more replies possible.
Where to now? Try our up-to-date Free Adaptive GMAT Club Tests
for the latest questions.
Still interested? Check out the "Best Topics" block above for better discussion and related questions.
Thank you for understanding, and happy exploring!
