Answer : 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.

Total number of ways = 5 × 5 × 5 × 5 = 625
So for first letter i.e. we have 5 ways Similarly for,

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