Mr. and Mrs. Doran have a genetic history such that the probability that a child being born to them with a certain trait is 67%. If they have five children, what is the probability that at least three of their five children will have that trait? Round your answer to the nearest thousandth.

Answer 1

at least 3 of 5
----> could be 3, or could be 4, or could be 5
Prob(trait) = .67
prob(not trait) = .33

prob(your event)
= C(5,3)(.67^3)(.33^2) + C(5,4)(.67^4)(.33) + C(5,5)(.67^5)
= 10(.67^3)(.33^2) + 5(.67^4)(.33) + (.67^5)
= .....