In a certain town, the judge is suspected of unfair jury selection. The population in the area is 80% ethnic Hmong, yet on average he only has two Hmong on a 12-member jury. Assuming fair selection, what is the expected number of Hmong, and what is the variance?
The probability that any particular person is from the Hmong tribe is p = 0.8; the number of "trials" is n = 12. The formula for the expected mean (in this case, the expected number of Hmong) is np. You should get an answer of "between nine and ten" being Hmong.
The formula for the variance, given probability p and a number of trials n, is np(1 - p). In this case, p = 0.8 and n = 12.
Yeah, the guy seems "guilty as charged".