Posted by Erika Chicas on Wednesday, December 5, 2012 at 4:40pm.
You can use the binomial distribution:
P = nCs*p^s*(1-p)^n(-s) where P is the probability we are hanting for, n = 15 is the size of a sample, s is the number of registered voters of 15 people, and p = 0.3 (30%) is the proportion of registered voters in the area.
a) P(3 of 15) = 15!/(15-3)!3!*(0.3)^3*(1 -0.3)^(15 -3) = 455*0.027*0.01384 = 0.17 or 17%;
b) to get results for "at most 3 of the 15 people", you have to apply the above approach four times:
P(0 of 15) =
P(1 of 15) =
P(2 of 15) =
P(3 of 15) =
then add these four probabilities together => P(at most 3 of 15);
c) I believe that we cannot because the sample of 15 people is too small (the critical size ia about 30 items).
thank you....!!!
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