Chance calculation.
#2
Well I thought I would have a try at this, no idea if I got it correct but I am fairly sure I am there.

Firstly, I organised all the different combinations of possibilities that occur with only 2 of the 5 being red marbles. This I completed with a probability tree.

I got:
1. p(R,R,W,W,W)
2. p(R,W,R,W,W,)
3. p(R,W,W,R,W)
4. p(R,W,W,W,R)
5. p(W,R,R,W,W)
6. p(W,R,W,R,W)
7. p(W,R,W,W,R)
8. p(W,W,R,R,W)
9. p(W,W,R,W,R)
10. p(W,W,W,R,R,)

Now after this, I calculated the overall probabilites of each of these occurences.

For example, No. 1 would look like this:

3/10 x 2/9 x 7/8 x 6/7 x 5/6 = 1/24.

Interestingly, each of these come to a total of 1/24 and so in the end you get 10/24 which of course simplifies to 5/12.

I figure this may be the answer as it is a nice, even fraction that looks right - typical of school given questions.

My final answer is 5/12.


Messages In This Thread
Chance calculation. - by Zealord - 11-01-2012, 12:57 PM
RE: Chance calculation. - by Adman - 11-01-2012, 01:24 PM
RE: Chance calculation. - by Zealord - 11-01-2012, 01:37 PM
RE: Chance calculation. - by Adman - 11-01-2012, 01:40 PM

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