Mother, father and son line up at random for a family picture. Find P(A/B), if A and B are defined as follows:

A = Son on one end, B = Father in the middle

Total number of ways in which mother (M), Father(F) and Son(S) can be lined up at random in one of the following ways:

MFS, MSF, FMS, FSM, SFM, SMF

We have, A = {SMF, SFM, MFS, FMS} and B = {MFS, SFM}