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B
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Difficulty:
55%
(hard)
Question Stats:
61% (02:02) correct
39%
(01:45)
wrong
based on 155
sessions
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If \(a*b = −8\), what is the value of \(a + b\)?
(1) \(a − b = 6\)
(2) \(a*b^2 = 32\)
Are You Up For the Challenge: 700 Level Questions
(1) \(a − b = 6\)
(2) \(a*b^2 = 32\)
Are You Up For the Challenge: 700 Level Questions
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
25 Nov 2019, 21:24
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If \(a*b = −8\), what is the value of \(a + b\)?
(1) \(a − b = 6\)
This will clearly give us two values....a=b+6
So \(a*b=b(b+6)=-8.......b^2+6b+8=0...(b+4)(b+2)=0\)
Two cases
b=-4, a=2...a+b=-4+2=-2
b=-2, a=4...a+b=4-2=2
Insuff
(2) \(a^2*b = 32.......a*(a*b)=32.....a*(-8)=32.....a=-4\)
So b = 2 and a+b=-4+2=-2
Suff
B
However the values of b differs in both statements. It should have been \(a*b^2=32\)
(1) \(a − b = 6\)
This will clearly give us two values....a=b+6
So \(a*b=b(b+6)=-8.......b^2+6b+8=0...(b+4)(b+2)=0\)
Two cases
b=-4, a=2...a+b=-4+2=-2
b=-2, a=4...a+b=4-2=2
Insuff
(2) \(a^2*b = 32.......a*(a*b)=32.....a*(-8)=32.....a=-4\)
So b = 2 and a+b=-4+2=-2
Suff
B
However the values of b differs in both statements. It should have been \(a*b^2=32\)
26 Nov 2019, 09:31
Kudos
Bookmarks
Bunuel
(1) \(a − b = 6\) insufic
\(a − b = 6…a=6+b…b(6+b)=-8…b^2+6b+8=0…(b+4)(b+2)=0\)
\((b,a)=(-4,2);(-2,4)…(a+b)=(-2;2)\)
(2) \(a^2*b = 32\) sufic
\(a^2*b = 32…a(ab)=32…a=32/(-8)=-4…b=2…a+b=-2\)
Ans (B)
*note: if a^2b=32 then a^2>0 and b>0; but (1) b=-4,-2… so there is something wrong with (2).
