We have two cases to deal
(a) with repetition allowed.
(b) with repetition not allowed.
now list for:
Case 1: aa,ab,ba,ac,ca,ad,da,bb,bc,cb,bd,db,cc,ed,dc,dd,i.e., there are 16 possibilities.
Case 2: ab,ba,ac,ca,ad,da,bc,cd,bd,db,cd,dc,ie., there are 12 possibilities.
We have senn all the possibilities in both cases.
To count the number of permutations without actual listing of the arrangements, we use the product rule as a technique.
We have two tasks to perform-namely filling up the first slot in the arrangement and filling up the second slot in the arrangement.
Case 1: Repetition allowed
Case 2: Repetition not allowed.
