# Thread: number of combinations

1. ## number of combinations

Please tell how you arrived there soi understand it, that is the most imporant thing.

How many ways can sierra select 3 movies to rent from the top 10 rentals?
A.720 ways, B.240 C. 90 ways D.120 ways

2. I think it's 10 chose 3. That is, $\frac{10!}{(10-3)!3!}=120$. To do it, I didn't think a lot. I mean the formula I gave you is very well known and useful in cases like yours here. It means, if you have 10 elements, how many ways are they if you want to pick 3 of them? This is exactly your problem. So I guess you'll get used to it after having done every kind of problems.
More generally, if there is a total of n element and you want to pick up m elements, the total possibilities are $\frac{n!}{(n-m)!m!}$. You should learn this formula and check out your notes, it is probably there and well explained.

3. Thank you

4. Originally Posted by phil2611
Thank you

hello me