Permutations And Combinations Question 173

Question: Number of ways in which a lawn-tennis mixed double be made from seven married couples if no husband and wife play in the same set is

Options:

A) 240

B) 420

C) 720

D) none of these

Show Answer

Answer:

Correct Answer: B

Solution:

  • [b] We first select 2 man out on 7 in $ ^{7}C_2 $ ways. Now we exclude the wives of these two selected men and so select 2 ladies form remaining 5 ladies in $ ^{5}C_2 $ ways. Let A, B be two men and X, Y be the ladies playing in one set. Then we can have (i) A and X plying against B and Y. (ii) A and Y playing against B and X. Then the total number of ways is $ ^{7}C_2{{\times }^{5}}C_2\times 2=21\times 10\times 2=420 $ .



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