Given: We have 4 letters and 5 letter boxes

To Find: Number of ways of posting letters.

One letter can be posted in any of 5 letter boxes.

We have to assume that all the letters are different.

So for first letter i.e. , we have 5 ways

Similarly for,

Total number of ways = 5 × 5 × 5 × 5 = 625

In 625 ways 4 letters can be posted in 5 letter boxes.