Question

In how many ways can three letters be posted in four letterboxes in a village? If all the three letters are not posted in the same letterbox, find the corresponding number of ways of posting.

Answer 1

We can post the first letter in 4 ways and 2nd too in 4 ways, as well as the third. Therefore the total number of ways is 4 x 4 x 4 = 64.
All the three letters can be posted in any of the four letter boxes in 4 ways.
Hence the corresponding number when all are not posted in the same letter box is 64 - 4 = 60.