How to do ncr on calculator?

You are taking a week-long trip and decide to bring 4 books from your collection of 25 books. How many different groups of 4 books can be selected from your collection?

Here, you only care about which four books are chosen, not the order. Thus, a combination can be used to answer this question: C(25, 4) or “25 choose 4”.

In this case, the first number is 25.

You can use the right arrow to select the menu at the top.

To select 3: nCr, you can either highlight the 3 or just press the 3 button.

We are finding C(25,4), so the second number is 4.

From this, we see that there are C(25, 4) = 12,650 different groups of 4 books that could be selected. This may seem like the answer is too large, but if you start thinking about how only one book needs to be different for the group of 4 books to be considered a different group, it begins to make more sense.

You can also use the formula to calculate a combination. You can review this, and more about combinations in general, below.

Counting with combinations