## anonymous 5 years ago A bag of marbles contains 8 red marbles and 5 green marbles. Three marbles are drawn at random at the same time. Find the probability that all three are red.

1. anonymous

8 out of 13

2. anonymous

${{8 \choose 3}\over {13 \choose 3}}$

3. anonymous

I assume you're familiar with choose notation.

4. anonymous

Who me?

5. anonymous

Well either you, or the original poster. Whomever wants to read/understand my answer.

6. anonymous

it's not 8 out of 13 though. That'd be about 61 percent

7. anonymous

Well yours is eight thirds over thirteen thirds right?

8. anonymous

no. it's choose notation. ${n \choose k} = {n! \over k!(n-k)!}$

9. anonymous

Ok yepp then i have no clue lol

10. anonymous

that's ok. it's a fun thing to learn about.

11. anonymous

I'd rather stay away from the complicated stuff if you can do it the easy way i choose that.

12. anonymous

Basically it boils down to : How many different ways can we pick 3 red marbles from a set of 8 red marbles. Then we divide that by the number of different ways we can choose 3 marbles from a bag of 13 marbles.

13. anonymous

mhm.. I did that in like 4th grade so i really dont remember it lol

14. anonymous

I'm not sure it's the same as what you're remembering.. But in any case there are 56 different ways you can pick 3 red marbles from a set of 8 red marbles.

15. anonymous

And there are 286 ways you can pick any 3 marbles from a bag of 13 marbles.

16. anonymous

ugh huh..

17. anonymous

so 56/286 = .1958 or 19.6%

18. anonymous

Is the probability you will grab exactly 3 red marbles.

19. anonymous

I get it now, thank you.

20. anonymous

This function is often built into calculators as the C function

21. anonymous

Are you really smart brain wise or calculator wise or just incredibly smart period?

22. anonymous

hrm.. tough one to answer. Probably I have just taken a lot of math classes. ;)

23. anonymous

Oh mmk i see.

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