How many ways can three letters be posted in 5 mail boxes if each mail box can receive 1 letter only
If each mailbox can receive only one letter, and there are three letters to be posted, there are 5 options for the first letter, 4 options for the second letter (as one mailbox has already been filled with the first letter), and 3 options for the third letter (as two mailboxes have already been filled with the first two letters).
Therefore, the total number of ways three letters can be posted in 5 mailboxes is:
5 * 4 * 3 = 60.