a) OK, this is a binomial distribution, with Pr(fling) = 0.2 and 9 cases (n=9). So the probability of 0 adults doing a fling in a sample of 9 can be found using the pdf of the binomial distribution at k=0, with n=9 and p=0.2 (k=outcomes, n=trials, p=prob. each trial is the outcome).
For example using binom.dist function in Excel you get: binom.dist(0,9,0.2,0) = 0.1342
b) This is just the inverse of the first question! If at least one person has done it, that's the opposite of "zero people have done it". So the answer is just 1-0.1342 = 0.8658.
c) No more than two people means 0 or 1 people have done it. We could either add the probability of 1 person [ binom.dist(1,9,0.1,0) = 0.3020 ] to 0.1342, or directly calculate the cumulative probability up to 1 [ binom.dist(1,9,0.1,1) ]. In both cases we'll get the answer 0.4362.
Hope this helped!
Feb 27th, 2015
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