Dropping letters in post boxes In how many different ways can 5 letters be dropped in 3 different post boxes if any number of letters can  be dropped in all of the post boxes?

The first letter can be posted in any of the 3 post boxes. Therefore, it has 3 choices.
Similarly, the second, the third, the fourth and the fifth letter can each be posted in any of the 3 post boxes.
Therefore, the total number of ways the 5 letters can be posted in 3 boxes is 3*3*3*3*3
= 3^5
