Probability 1 Question 19

27. In how many ways three girls and nine boys can be seated in two vans, each having numbered seats, 3 in the front and 4 at the back? How many seating arrangements are possible if 3 girls should sit together in a back row on adjacent seats? Now, if all the seating arrangements are equally likely, what is the probability of 3 girls sitting together in a back row on adjacent seats?

(1996,5 M)

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Answer:

Correct Answer: 27. 0.62

Solution:

  1. We have 14 seats in two vans and there are 9 boys and 3 girls. The number of ways of arranging 12 people on 14 seats without restriction is

14P12=14!2!=7(13!)

Now, the number of ways of choosing back seats is 2 . and the number of ways of arranging 3 girls on adjacent seats is 2(3!) and the number of ways of arranging 9 boys on the remaining 11 seats is 11P9 ways.

Therefore, the required number of ways

=2(23!)11P9=43!11!2!=12!

Hence, the probability of the required event

=12!713!=191



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