The word "climbing" has 8 letters, so there are [tex]8![/tex] permutations of all the letters.
Nevertheless, the letters are not unique: there are 2 I's. This means that, if we start from a given word and we exchange the positions of the two I's, we'd still get the same word. So, we have to divide the number of possible permutations by [tex]2![/tex], because for any given permutation there are two identical words, given by the interchange of the I's.
So, the number of possible words is
[tex]\dfrac{8!}{2!} = \dfrac{8\times7\times6\times5\times4\times3\times2}{2}=8\times7\times6\times5\times4\times3=40320[/tex]
