Say I have a set like a,b,c,d,e,f,g,h,i,j

And, I pick five like abcde

how many ways can I pick 5 such that it differs from the original by n?

For example by two like bacde, or fgcde? It is driving me nuts since it changes based on the use of one of the original characters. In other words, there are five ways to have the first two characters differ that start with 'j,' but 6 ways to have the first two characters differ that start with 'b.'