Posted by ryan on Saturday, May 1, 2010 at 4:16pm.
Pr(7 right, 13 wrong)= .25^7 * .75^13 * number of ways
the number of ways is 20!/(7!13!)
((20 !) / ((7 !) * (13 !))) * (.25^7) * (.75^13) = 0.112406195
check my thinking.
And here are some probability tutorials you might find handy:
http://search.yahoo.com/search?fr=mcafee&p=probability+tutorial
Sra
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