In how many ways can the six letters of the word "mammal" be arranged in a row?
Since there are 3 "m"s and 2 "a"s in the word "mammal", we have:
6!/3!2!=60
There is one "L" in "mammal", but it does not affect the answer, since 1! = 1
http://www.intmath.com/counting-probability/3-permutations.php