You have the first season of your favorite television show on a set of DVDs. The set contains 10 episodes. You have time to watch 2 episodes. How many combinations
of 2 episodes can you watch?

There are 45 combinations.

Step-by-step explanation:

If the order in which you watch the episodes does not matter, then we can use the combinatory defined as:

If we have N elements, and we want to make groups of K elements, we have

combinations.

In this case, we have a total of N = 10 episodes, and we want to make groups of  K = 2.

Then we have:

There are 45 combinations.