How many ways are there to rearrange the letters of STOP, so that no letter remains in the same place?
If I undestand your question, then there are 9 such arrangements as follows:
STOP: [{O, P, S, T} , {O, P, T, S} , {O, S, P, T}, {P, O, S, T}, {P, O, T, S} , {P, S, T, O} , {T, O, P, S}, {T, P, S, O}, {T, S, P, O} ]
