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!!!

What have you tried so far?

 

Although this may be giving too much away, have you covered Bernoulli trials yet?

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 ???

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, 201312 yr by John

A ok... Thank you very much!!!

You're welcome. Glad I could help.