Question is: "If you roll a fair coin 10 times what is the expected product of number of heads and number of tails?" Someone answered 25 at at glassdoor.com. My answer would be: E(k(10-k)) where k is the rv representing the number of heads thrown. = 10E(k) - E(k^2) = 10*mean - (var + mean^2) where mean = np = 10*0.5 = 5, and var = npq = 10*.5*.5 = 2.5 (these are the formulas for the binomial distribution), thus, = 10*5 - (2.5 + 25) = 22.5 Who is correct? Thanks. Nick.