Exercise in Probability!!!!

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evinda

Junior Member
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Apr 13, 2013
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Hey!!! I need some help at the following exercise... :confused:

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!!!
 
evinda said:
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?
Click to expand...


\(\displaystyle 1-\sum\limits_{k = 0}^3 {\binom{20}{k}{{\left( {0.1} \right)}^k}{{\left( {0.9} \right)}^{20 - k}}}\)

Now please, you reply with an explanation why that works.
 
Hmmmm....The probability is P(X>3)=1-P(X<=3)=1-(P(X=0)+P(X=1)+P(X=2)+P(X=3)),where P(X=i)={20 choose i}*0,1^i*0.9^(20-i)...Right??? :D
 
evinda said:
Hmmmm....The probability is P(X>3)=1-P(X<=3)=1-(P(X=0)+P(X=1)+P(X=2)+P(X=3)),where P(X=i)={20 choose i}*0,1^i*0.9^(20-i)...Right??? :D
Click to expand...

Well thank you. And yes: it is the complement of \(\displaystyle X=0,~1,~2,\text{ or }3~.\)
 
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