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The number of permutations of n different things, taken r at a time, in which P (r ≤ n − p) particular things will never occure is : (a) P (n − p, r) × P (n, n − p) (b) P (n, r) × P (n, p) (c) P (n, r) − P (n, p) (d) P (n − p, r) |
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Answer» Correct option (d) P (n − p, r) Explanation: Since p particular things out of n different things is never taken. So, we have to determine the number of ways in which r places can be filled with (n − p) distinct things. Clearly, the number of such arrangements is n − p Pr = P (n − p, r), where P (r ≤ n − p) |
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