Difference between permutation and combination

The difference is that permutation is an arrangement where order is important while combination is a selection and order is not important. Think of a sandwich made from a slice of bread, an omelette and salad. You can arrange the three ingredients in the following order (assume you are laying the sandwich on the plate); a) bread, omelette,salad b) bread, salad, omelette c) salad,bread, omelette d) salad, omelette, bread e) omelette, bread, salad f) omelette,salad, bread The above is 6 arrangements (permutations). Now, assume 6 people ordered (a) to (f) sandwiches for breakfast, would they be right to say they ate 6 different types of sandwiches? of course NOT!It is just one COMBINATION (selection) of sandwich.