Posted by Student on Sunday, August 24, 2008 at 11:00pm.
The probability of three purchases after seven customer visits is
P(3) = (0.6)^3*(0.4)^4*C(7,3)
where C(7,3) is the binomial coefficient
C(7,3) = 7!/(4!*3!) = 70
I get 0.387 for the answer.
For P(n>4), add P(5), P(6) and P(7)
For an explanation of how the probability relates to the binomial coefficient, see
http://en.wikipedia.org/wiki/Binomial_coefficient
How do you get 70. When I calculate the formula I get 35.
7!/(4!*3!) = 5*6*7/(1*2*3)= 210/6 = 35
You are right
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