Posted by **kim** on Friday, July 27, 2012 at 1:43pm.

There are 6 pairs of black socks and 6 pairs of white socksWhat is the probability to pick a pair of black or white socks when 2 socks are selected randomly in darkness?M

- Math -
**Reo**, Friday, July 27, 2012 at 1:57pm
I think it's nCk which the total of socks would be 12 since we have 6 whites and 6 black. you would have to choose 2. in that case order does not matter and we use the combination formula 12C2 = 66 possible ways.

- Math -
**Reiny**, Friday, July 27, 2012 at 2:18pm
could be either BB or WW

Prob(BB) = (6/12)(5/11) = 5/22

which is the same as the prob(WW)

so prob of either WW or BB = 2(5/22) = 10/22

(note only other cases are WB and BW

and the prob of those = 2(6/12)(6/11) = 2/11 or 12/22

and prob of all cases = 10/22 + 12/22 = 22/22 = 1 )

All is good!

- typo - Math -
**Reiny**, Friday, July 27, 2012 at 2:21pm
correction in 3rd last line, should be

and the prob of those = 2(6/12)(6/11) = **6/11** or 12/22

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