1.

20 persons are arranged along a round circle. If 4 persons are selected at random, find the probability that (a) all the selected 4 are not consecutive (b) no two of the selected 4 are consecutive (c) a specified person must always be selected and no two of the selected 4 are consecutive. (d) exactly two persons of the selected 4 are consecutive.

Answer»


ANSWER :(a) `1 - (20)/(.^(20)C_(4))`
(b) `(2275)/(.^(20)C_(4))`
(c) `(.^(15)C_(3))/(.^(20)C_(4))`
(d) `(2100)/(.^(20)C_(4))`


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