Combinaciones (Probabilidad)

Combinations. Now we're going to look at the topic of combinations. The rule for calculating combinations is as follows. We have that the number of combinations of r elements selected from a list of n different elements is. We put the combination c where we have a total of n elements. We put in n and we are going to form

groups or select r elements. Then we put r. This will be equal to having n factorial divided by r factorial multiplied by n - r factorial. So what we're saying here is that if we want to form groups of r elements, taking from a total of n elements, we're going to expand this formula.

Remember that factorial is, for example, 5 factorial, which is equal to 5 * 4 * 3 * 2 * 1. 3 factorial is equal to 3 * 2 * 1. And by definition, 0 factorial is equal to 1. Combinations are used when the order in which the elements appear is not important. Let's look at this with some

examples. So, we have said that in the case of combinations, the order in which the elements appear does not matter, but in permutations it does matter. If we have A, B, C, which are three letters. Then if we have another BCA selection, we can see that both selections have the same letters , but since in

permutations the order does matter, then these two selections are different. In this case, we have two different permutations. On the other hand, if we are talking about combinations, we again have ABC and then BCA. Since we have the same letters in both selections and in the case of combinations the order does not matter,

then these two selections are considered equal. So this combination is the same as this combination. Therefore, we say here that it is the same combination, since the order does not matter. Well, with this we have that in combinations the order does not matter. Therefore, the order in which the selected elements are arranged does not matter