Or, if we are asked to find how many ordered things from a collection, it’s permutation. So if we are asked to just choose a few things from a collection, it’s combination. In order to find out the number of permutation we first need to find out the number of combination, i.e permutation = combination + no. In permutation we need to choose then need to order them, but choosing means combination. But in permutation there are two steps : choose & order. In combination, there’s only one step : to choose. So combination is easier than permutation. But in permutation along with choosing them from a collection we need to order them. For our example 3P2 = 6.įrom the above description, we can see that, in combination we just need to choose things from a collection. To permute r thing from a collection of n things is expressed as nPr. So the permutation will be ab, ba, ac, ca, bc, cb. For the previous example, to select two letter from these three: a,b,c. Like ab & ba are two different permutation. The items we select may be same, but because of their ordering they can be two different permutation. Permutation is a way of selecting some items from a collection in a sequence or order. Permutation is a bit different from combination. In how many ways we can choose r things from a total of n things, is known as the combination and expressed as nCr. For our example 3C2 = 3. So we can choose a,b or a,c or b,c i.e we can choose two letter in three ways. We want to choose two letter from these three. For example, suppose we have three letter: a,b,c. Like we have some items, in how many ways we can choose a few items (a fixed number) from them is called combination. Combination is a way of selecting some items from a collection. is it a permutation problem / is it a combination problem? To understand the problem criteria we first need to understand the basic concepts of permutation & combination.įirst, start with combination. But it’s easy to get confused between this two things i.e. It is very much used in our day-to-day life. Permutation-Combination, a very interesting & important part of mathematics.
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