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Permutations And Combinations

Question
CBSEENMA11014034

A class has 30 students. In how many ways can three prizes be awarded so that:

(a) no students get more than one prize?

(b) a student may get any number of prizes?

Solution

(a) Number of ways in which the first prize can be awarded = 30
rightwards double arrow                             m = 30
Number of eligible students for the second prize = 29
∴   Number of ways in which second prize can be awarded = 29
rightwards double arrow                         n = 29
Number of ways in which the third prize can be awarded = 28
rightwards double arrow                        P = 28
∴   By fundamental principle of counting, the total number of ways of awarding the three prizes.
              = straight m cross times straight n cross times straight p space equals space 30 cross times 29 cross times 28 space equals space 24360.
(b) Number of students = 30
Number of ways in which the first prize may be awarded = 30
rightwards double arrow                    m = 30
Number of students eligible for the second prize = 30 (∵ A student may get any number of prizes)
Number of ways in which the second prize can be awarded = 30
rightwards double arrow                             n = 30
Similarly, number of ways in which the third prize can be awarded = 30
rightwards double arrow                            p = 30
By fundamental principle of counting, the number of ways in which the three prizes can be awarded
                               = space space space space space straight m cross times straight n cross times straight p equals 30 cross times 30 cross times 30 equals 27000.

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