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28 Jul 2016, 12:00
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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:
35%
(medium)
Question Stats:
72% (01:42) correct
28%
(01:58)
wrong
based on 206
sessions
History
Date
Time
Result
Not Attempted Yet
If a, b, c, and d are positive numbers, and \(\frac{a}{b} = \frac{c}{d}\), what is the value of \(\frac{a}{b}\)?
Statement #1: \(\frac{2a}{c} - \frac{b}{d} = \frac{b}{d}\)
Statement #2: \(25c^2 = 8d^2\)
This DS questions contains a tautological statement. There is a subtle logical difference between deciding a statement is tautological vs. merely insufficient. For a full discussion, as well as the OE for this particular question, see
GMAT Data Sufficiency Logic: Tautological Statements
Mike
Statement #1: \(\frac{2a}{c} - \frac{b}{d} = \frac{b}{d}\)
Statement #2: \(25c^2 = 8d^2\)
This DS questions contains a tautological statement. There is a subtle logical difference between deciding a statement is tautological vs. merely insufficient. For a full discussion, as well as the OE for this particular question, see
GMAT Data Sufficiency Logic: Tautological Statements
Mike
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
28 Jul 2016, 12:13
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Statement 1 says the same thing what question stem has got
statement 2 : c/d = root(8/25) ==> + or _ (root(8/25))
since all the numbers are positive, + rrot(8/25)
B is the answer
statement 2 : c/d = root(8/25) ==> + or _ (root(8/25))
since all the numbers are positive, + rrot(8/25)
B is the answer
28 Jul 2016, 14:34
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mikemcgarry
Statement #1: \(\frac{2a}{c} - \frac{b}{d} =\frac{b}{d}\)
From the question stem:
\(ad = bc\\\\
\frac{a}{c} = \frac{b}{d}\)
The statement is equivalent to \(2 \times \frac{b}{d} - \frac{b}{d} =\frac{b}{d}\), which is a tautology, no additional information is provided.
Not Sufficient
Statement #2: \(25c^2 = 8d^2\)
\(\frac{25}{8} = \frac{c^2}{d^2}\)
\(\frac{5}{2\sqrt{2}} = \frac{c}{d} = \frac{a}{b}\)
Sufficient
(B) statement 2 alone is sufficient, but statement 1 alone is not sufficient to answer the question
