Posted by todd on Sunday, February 10, 2008 at 10:27pm.
Pinworm infestation commonly found in kids can be treated with the drug pyrantel pamoate. Research shows the treatment is effective about 90% of cases. The drug is administered to 25 kids.
What is the probability that exactly 23 of them are cured?
What is the prob. that more than 23 of them are cured?
What is the prob. that at most 23 of them are cured?
What is the expected # of kids that will be cured using this treatment?

statistics  economyst, Monday, February 11, 2008 at 9:15am
I would solve this problem using basic combinatorial methods. Hint: an EXCEL spreadsheet is very helpful in these types of problems.
The probability that 23 are cured is exactly equal to the probability that 2 are not cured. So, 25choose2 is 24*25/2 = 300. So, the probability of seeing exactly 2 not cured is 300*(.9^23)*(.1^2) = 26.588%.
Take it from here to solve the rest of the problems.