A few examples:

**Suppose you have forgotten a password with 5 characters.**

You only remember:

➢ the 5 characters are all distinct

➢ the 5 characters are B, D, M, P, Y

If you want to try all possible combinations, how many of them in total?

What if the password is in the form adaaada?

➢ a means letter, d means digit

➢ all characters are all distinct

➢ the 5 letters are B, D, M, P, Y

➢ the digit is either 0 or 1

How many combinations are there?

What if the password is in the form adaaada?

➢ a means letter, d means digit

➢ all characters are all distinct

➢ the 5 letters from B, D, M, P, Y, Z, W

➢ If B appears in the password, D will not be allowed to appear

➢ the digit is either 0 or 1

How many combinations are there?