The difference is that permutations take order into account whereas combinations do not. For example, if you are looking to choose 3 people from 5 then the number of choices (combinations) is ₅C₃ = 10 whereas if you want to form a line-up of three people from 5 then order is important and you can do this in 5x4x3 = 60 ways. In general _nP_k = k!_nC_k where _nP_k is the number of permutations of k objects from a set of n distinct objects and _nC_k is the number of combinations of k objects from a set of n distinct objects (and k!, k factorial,is k×(k-1)...×3×2×1).

Penny