Determine the number of ways to arrange the letters of the word RADII.
I know that if I had five distinct letters, I could arrange them in 5! = 120 ways. But since the letter I appears twice, I have to account for the fact that swapping the two I's does not create a new arrangement. So I have to divide by the number of ways to arrange the two I's, which is 2! = 2. Therefore, the number of ways to arrange the letters of the word RADII is 5! / 2! = 120 / 2 = 60.

