Conditional Probability: 5 brown 7 blue 8 black socks are...

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stacey

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May 6, 2007
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5 brown 7 blue 8 black socks are in drawer total 20 socks
What is the probability of taking two brown socks from the drawer?
I understand dependent probability
P(Brown and Blue and Black)

How does this work?

P(brown)/20 or do you P(br)*P(bl)*P(black)

5/20*7/20*8/20= 280/8000 i think this is wrong!

I got the second half
suppose 3 pr socks were taken
8/20*5/19*7/18= 280/6840 7/171
 
I am going to assume you are going to draw 2 socks - one after the other (this really does not matter but easier to understand) - AND YOU WANT BOTH OF THOSE TO BE BROWN

Probabiliy of first brown socks = 5/20

Now you are left with 4 brown socks in the drawer with 19 socks.

Probabiliy of second brown socks = 4/19

Can you finish it now.....
 
stacey said:
5/20 *4/20= 20/380 or 1/19 ;)
Click to expand...
Good work, stacey; typo: 4/19 : QUICK: go edit it :shock:

Try this: 200 white socks, 200 black socks, all mixed up in drawer:
if you pull out 3 at random, what is probability that you'll get a matching pair?
 
200 White
200 Black
total 400
pull out three random probability of getting a match?
200wC3 /400C3 200blC3/400C3

1313400 * 1313400/10586800

200 Chose 3 = 1313400 200 chose 3 = 1313400

400 chose 3 = 10586800

answer 162940.60

hmmm? i will be thinking about this one in my sleep
 
GOTCHA!

If you pull 3 socks, you're SURE to get a matching pair: try it :lol:
 
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