15 persons among whom are A and B, sit down at random at round table.

1.	15 persons among whom are A and B, sit down at random at round table. The probability that there are exactly four persons between A and B is(a) 9!/14! (b) 10!/14! (c) 2.9!/14! (d) 2.13!/14!
Answer» Correct option(d) 2.13!/14! Explanation: 15 persons can be seated round a table in 14! ways. If 4 persons are to be included between A and B, they can be arranged in ¹³C₄ x 4! ways, now total number of arrangements is ¹³C₄ x 4! × 9! × 2! = 2.13! Hence the probaility is 2.13!/14! = 2/14 = 1/7

15 persons among whom are A and B, sit down at random at round table. The probability that there are exactly four persons between A and B is(a) 9!/14! (b) 10!/14! (c) 2.9!/14! (d) 2.13!/14!

Answer»

Correct option(d) 2.13!/14!

Explanation:

15 persons can be seated round a table in 14! ways. If 4 persons are to be included between A and B, they can be arranged in ¹³C₄ x 4! ways, now total number of arrangements is ¹³C₄ x 4! × 9! × 2! = 2.13!

Hence the probaility is 2.13!/14! = 2/14 = 1/7

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15 persons among whom are A and B, sit down at random at round table. The probability that there are exactly four persons between A and B is(a) 9!/14! (b) 10!/14! (c) 2.9!/14! (d) 2.13!/14!

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