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09 Feb 2022, 05:30
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B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
15%
(low)
Question Stats:
84% (01:09) correct
16%
(01:19)
wrong
based on 55
sessions
History
Date
Time
Result
Not Attempted Yet
Is \(ab < 8\) ?
(1) \(a < 4\) and \(b < 3\)
(2) \(a^3 < 8\) and \(b - 4 = 0\)
(1) \(a < 4\) and \(b < 3\)
(2) \(a^3 < 8\) and \(b - 4 = 0\)
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
kungfury42
Joined: 07 Jan 2022
Last visit: 31 May 2023
Posts: 580
Own Kudos:
Given Kudos: 724
Schools: NUS '25 (A)
GMAT 1: 740 Q51 V38
GPA: 4
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09 Feb 2022, 15:38
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Statement 1:
If \(a<4\) and \(b<3\) then \(a*b<12\)
Whether \(a*b<8\) we cannot comment. \(a*b\) could be \(9\) or could be \(6\), could be literally anything less than \(12\).
Clearly insufficient.
Statement 2:
\(a^3<8\) or \(a<2\)
\(b-4=0\) or \(b=4\)
\(a*b<8\) Sufficient.
Hence, statement 2 alone is sufficient, option B.
Posted from my mobile device
If \(a<4\) and \(b<3\) then \(a*b<12\)
Whether \(a*b<8\) we cannot comment. \(a*b\) could be \(9\) or could be \(6\), could be literally anything less than \(12\).
Clearly insufficient.
Statement 2:
\(a^3<8\) or \(a<2\)
\(b-4=0\) or \(b=4\)
\(a*b<8\) Sufficient.
Hence, statement 2 alone is sufficient, option B.
Posted from my mobile device
14 Feb 2022, 15:24
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Bunuel
Breaking Down the Info:
When we see products of variables, we must pay attention to the signs. Negative \(a\) and negative \(b\) can produce a product that is greater than 8.
Statement 1 Alone:
Even with positive only a and b, we would have \(ab < 12\), which is insufficient.
Statement 2 Alone:
The first inequality can be simplified to \(a < 2\), since we have an odd power. We are also given b = 4, so we can multiply both sides by b to get \(ab < 2b = 8\). Then statement 2 is sufficient.
Answer: B
