Permutations and Combinations 5 Question 2

2. There are four balls of different colours and four boxes of colours, same as those of the balls. The number of ways in which the balls, one each in a box, could be placed such that a ball does not go to a box of its own colour is…. .

(1992, 2M)

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Answer:

Correct Answer: 2. (9)

Solution:

  1. The number of ways in which the ball does not go its own colour box =4!111!+12!13!+14!

=4!1216+124=24124+124=9



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