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20 persons are arranged along a row and 4 of them 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) the first person of the linear arrangement must be selected and no two of the selected 4 are consecutive. (d) exactly three persons of the selected 4 are consecutive. (e) exactly two persons of the selected 4 are consecutive. |
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Answer» (B) `(.^(17)C_(4))/(.^(20)C_(4))` (C) `(.^(16)C_(3))/(.^(20)C_(4))` (d) `(272)/(.^(20)C_(4))` (e) `(2040)/(.^(20)C_(4))` |
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