A contest consists of finding all of the code words that can be formed from the letters in the name "ATARI". Assume that the letter A can be used twice, but the others at most once.

a. How many five-letter words can be formed?

b. How many two-letter words can be formed?

c. How many words can be formed?

Answers
a. 60
b. 13
c. 170

Can anyone explain how to get these answers?

If among n things, r1 are identical, and the rest are distinct, the number of permutations is n! / [(r1)! ]

a. Five letter words: = 5! / [2! ] = 60

You should be able to do the rest yourself.