pamelaover wrote:

I really didn't understand why we have to divide by 2 when we consider the "S" to the right or left.

How can we get in this magic number?

pamelaoverLet's say we have 3 letters, A, B ad C.

What are the different arrangements possible? 6 - ABC, ACB, BCA, BAC, CAB, CBA. Now, if we are asked, in how many such arrangements are C right of B? It is 3 - ABC, BCA, BAC, half of the total number of 6. So, when we are asked, in how many such arrangements, S is to the right of P, we can get that number by dividing the total number of arrangements by 2.