Question

In how many ways can 7 letters be posted in 4 letter boxes?

Answer 1

Each letter can be posted in any one of the 4 letter boxes.
Number of ways of posting one letter = 4
∴ Required number of ways of posting the 7 letters = 4$\times$4$\times$4$\times$4$\times$4$\times$4$\times$4 = $4^7$