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two-element?

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two-element?

by grandh01 » Wed Aug 15, 2012 4:04 pm
How many two-element subsets of {1,
2, 3, 4} are there that do not contain
the pair of elements 2 and 4?
(A) One
(B) Two
(C) Four
(D) Five
(E) Six
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by theCEO » Wed Aug 15, 2012 4:23 pm
grandh01 wrote:How many two-element subsets of {1,
2, 3, 4} are there that do not contain
the pair of elements 2 and 4?
(A) One
(B) Two
(C) Four
(D) Five
(E) Six
Total # of pairs = (4*3) / 2 = 6
No. of pair of 2 and 4 = 1
No of pair that do not contain 2 and 4 = 6 - 1 = 5
ans = d
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by Brent@GMATPrepNow » Wed Aug 15, 2012 7:24 pm
grandh01 wrote:How many two-element subsets of {1,
2, 3, 4} are there that do not contain
the pair of elements 2 and 4?
(A) One
(B) Two
(C) Four
(D) Five
(E) Six
Given the very small answer choices, students should consider just listing all of the possible subsets.
They are:
(1,2)
(1,3)
(1,4)
(2,3)
(3,4)

The answer is D Five

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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