5.

How many 3-digit numbers can be formed from the digits 1, 2, 3, 4 and 5 assuming that repetition of the digits is not allowed.

Number of ways in which place (x) can be filled = 5

                                           m = 5

Number of ways in which place (y) can be filled = 4      (∵ Repetition is not allowed)

                                           n = 4

Number of ways in which place (z) can be filled = 3      (∵ Repetition is not allowed)

                                           p = 3

∴ By fundamental principle of counting, the total number of 3 digit numbers formed

                                         = m x n x p = 5 x 4 x 3 = 60.