http://kaharris.org/teaching/425/Lectures/lec37.pdf "Fifty numbers are rounded-off to the nearest integer and the summed. Suppose that the individual round-off errors are uniformly distributed over (0:5; 0:5). What is the probability that the round-off error exceeds the exact sum by more than 3?" I don't understand how they calculate the variance where they get the 1/12 This isn't homework nor am I taking a class in statistics. I will however be taking an exam in statistics so I can credit for a class in statistics in May. Any help will be appreciated.