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15 Aug 2013, 02:22
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A
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
35%
(medium)
Question Stats:
68% (01:42) correct
32%
(02:09)
wrong
based on 383
sessions
History
Date
Time
Result
Not Attempted Yet
If ab > 0, does (a - 2)(b - 2) = 4 ?
(1) 2a + 2b = ab
(2) a = b
(1) 2a + 2b = ab
(2) a = b
I don't agree with OA here. Experts can you please confirm whether the OA is correct.
Reasoning for 2nd statement will be appreciated
Reasoning for 2nd statement will be appreciated
Pure algebraic questions like this one are no longer part of the GMAT Data Sufficiency syllabus.
For relevant Data Sufficiency questions, please check the Data Sufficiency forum:
Data Sufficiency Forum
Data Sufficiency Forum
blueseas
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15 Aug 2013, 02:36
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mridulparashar1
\(ab > 0\)
MEANS\(a,b\) have same signs and \(a,b\) is not equal to zero.
(1)\(2a + 2b = ab\)
\(2a+2b-ab=0\)
subtracting 4 from both sides
\(2a-ab-4+2b=-4\)
\(a(2-b)-2(2-b)=-4\)
\((a-2)(2-b)=-4\)
or
\((a-2)(b-2)=4\)
sufficient.
(2) \(a = b\)
let say \(a=b=2\) then \((a-2)(b-2) = 0\).....NO
let\(a=b=4\) then\((a-2)(b-2) = 4\).....YES
not sufficient
hence A
15 Aug 2013, 03:45
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If ab > 0, does (a - 2)(b - 2) = 4 ?
Does \((a - 2)(b - 2) = 4\)? Or: does \(ab-2a-2b+4=4\) --> does \(2a + 2b = ab\)?
(1) 2a + 2b = ab. Directly gives an YES answer to the question. Sufficient.
(2) a = b. The questions becomes: is \(2a+2a=a^2\)? --> is \(4a=a^2\)? --> is \(a=4\)? (discard a=0, since we know that \(a\neq{0}\) from ab>0). Since we don't know whether \(a=4\), then the statement is not sufficient.
Answer: A.
Hope it's clear.
Does \((a - 2)(b - 2) = 4\)? Or: does \(ab-2a-2b+4=4\) --> does \(2a + 2b = ab\)?
(1) 2a + 2b = ab. Directly gives an YES answer to the question. Sufficient.
(2) a = b. The questions becomes: is \(2a+2a=a^2\)? --> is \(4a=a^2\)? --> is \(a=4\)? (discard a=0, since we know that \(a\neq{0}\) from ab>0). Since we don't know whether \(a=4\), then the statement is not sufficient.
Answer: A.
Hope it's clear.
