# Combination with repetition and without repetition

It may seem funny that multiplying no numbers together gets us 1, but it helps simplify a lot of equations. But knowing how these formulas work is only half the battle. But how do we write that mathematically?

Let us say there are five flavors of icecream: How many ways can you choose 2 winners from 3? The next Node will discuss the general formula.

Notice that there are always 3 circles 3 scoops of ice cream and 4 arrows we need to move 4 times to go from the 1st combination with repetition and without repetition 5th container. Figuring out how to interpret a real world situation can be quite hard. Here is an extract showing row Pool Balls without order So, our pool ball example now without order is: When the order does matter it is a Permutation.

In other words, there are 3, different ways that 3 pool balls could be arranged out of 16 balls. For example, let us say balls 1, 2 and 3 are chosen. Here's how it works:

So it is like we are ordering a robot to get our ice cream, but it doesn't change anything, we still get what we want. It is often called "n choose r" such as "16 choose 3" And is also known as the Binomial Coefficient. And we can write it like this:. This is because there are 2 ways to order every 2-element combination.

Sometimes it's easier to go by an example first and make an abstraction after that. This is how lotteries work. In this order, we'd have nothing in the first urn, three in the second urn and two balls in the third urn.

These are the possibilites: How many ways can you choose 1 winner from 3 contestants? But how do we write that mathematically? Hide Ads About Ads. You distributed the fruits without separators but you don't know how to count them.

How many ways can combination with repetition and without repetition and second place be awarded to 10 people? Challenge How many ways can you choose 3 winners from 10 contestants? I'm not asking why the two expressions are the same, I know that. So, our first choice has 16 possibilites, and our next choice has 15 possibilities, then 14, 13, 12, 11, So we adjust our permutations formula to reduce it by how many ways the objects could be in order because we aren't interested in their order any more:.