mathmari Posted April 13, 2013 Posted April 13, 2013 Hey!!! I need some help at the following exercise...We have a box with balls and 10% of them are red. If we choose at random 20 balls with replacement, which is the probability to pick more than 3 red balls???Thanks in advance!!!
John Posted April 13, 2013 Posted April 13, 2013 What have you tried so far? Although this may be giving too much away, have you covered Bernoulli trials yet?
mathmari Posted April 13, 2013 Author Posted April 13, 2013 Do you mean: P(X>3)=1-P(X<=3)=1-(P(X=1)+P(X=2)+P(X=3)), where P(X=i)={20 choose i}*((0,1)^i)*((0.9)^(20-i)), i=1,2,3 ???
John Posted April 13, 2013 Posted April 13, 2013 (edited) Yes, almost. You'll also need to subtract the probability of getting zero red balls (which, of course, is a bit simpler to calculate). Edited April 13, 2013 by John
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