Question

In how many ways can $5$ letters be posted in $4$ letter boxes?

Answer 1

Since each letter can be posted in any one of the four letter boxes. So, a letter can be posted in $4$ ways. Since there are $5$ letters and each letter can be posted in $4$ ways. So, total number of ways in which all the five letters can be posted $=4\times 4\times 4\times 4\times 4=4^5$