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(Hi)

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- May 14th 2008, 03:55 PMphil2611number 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(Hi) - May 14th 2008, 04:17 PMarbolis
I think it's 10 chose 3. That is, $\displaystyle \frac{10!}{(10-3)!3!}=120$. 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 $\displaystyle \frac{n!}{(n-m)!m!}$. You should learn this formula and check out your notes, it is probably there and well explained. - May 14th 2008, 06:28 PMphil2611
Thank you

- May 14th 2008, 06:29 PMphil2611