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07 Jul 2025, 08:00
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No married couples: \(2^n\)
Only married couples: \(\frac{n!}{(\frac{n}{2}!)^2}\)
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
95%
(hard)
Question Stats:
51% (02:15) correct
49%
(02:43)
wrong
based on 319
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A certain company is forming a committee of n people to be chosen from n married couples, where n is a two-digit even number.
Select for No married couples the number of different committees that can be formed if no two people who are married to each other are allowed to serve on the committee, and select for Only married couples the number of different committees that can be formed if the committee must consist only of married couples. Make only two selections, one in each column.
| No married couples | Only married couples | |
| \(n!\) | ||
| \(n^2\) | ||
| \(2^n\) | ||
| \(\frac{n!}{2(n-2)!}\) | ||
| \(\frac{n!}{(\frac{n}{2}!)^2}\) | ||
| \(\frac{(2n)!}{(n!)^2}\) |
ShowHide Answer
Official Answer
No married couples: \(2^n\)
Only married couples: \(\frac{n!}{(\frac{n}{2}!)^2}\)
07 Jul 2025, 08:00
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Bunuel
GMAT Club Official Explanation:
Since the committee must not include any married couples, only one "representative" from each married couple can be selected. We are forming an n-person committee, so we must select n married couples that will each send one "representative" to the committee. The number of ways to choose n couples out of n is C(n, n) = 1.
For each of these n couples, there are two choices for the "representative": either husband or wife. This results in 2 * 2 * ... * 2 (n times) = 2^n possibilities.
Therefore, the total number of ways to form the committee is C(n, n) * 2^n = 2^n.
As for the committees that can be formed if the committee must consist only of married couples, we are choosing n/2 couples (which gives us n people) from n married couples. This is given by:
\(C(n, \frac{n}{2}) =\)
\(= \frac{n!}{\frac{n}{2}! * (n - \frac{ n}{2})!} =\)
\(= \frac{n!}{(\frac{n}{2}!)^2}\)
General Discussion
07 Jul 2025, 08:35
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Hi,
Given: Couples = n => Total People = 2n
Need to select = n (half)
No married couples: We need to select one from each couple
So 2 ways to select from each couple = 2 * 2 * 2 * ...... n times = 2^n
Only married couples: We need to select n/2 couples so that we get total n people
those n/2 couples will come from n couples in total = nC(n/2) = n!/(n/2!)(n-n/2)! = n!/(n/2!)^2
Cheers,
Keshav Sharma
Given: Couples = n => Total People = 2n
Need to select = n (half)
No married couples: We need to select one from each couple
So 2 ways to select from each couple = 2 * 2 * 2 * ...... n times = 2^n
Only married couples: We need to select n/2 couples so that we get total n people
those n/2 couples will come from n couples in total = nC(n/2) = n!/(n/2!)(n-n/2)! = n!/(n/2!)^2
Cheers,
Keshav Sharma
