An unfair 12-sided die x (because 1-8 come up 10% of the time each and 9-12 5% each) has mean 5.7 and standard deviation 3.195, and a fair 20-sided die y has mean 10.5 and standard deviation 5.766. (you can check these if you're interested, but use the rounded versions given here.) we roll both dice. let s be the sum. the mean of s is the standard deviation of s (to three places after the decimal) is let d be the difference y-x. the mean of d is .the standard deviation of d is .if we relabel the 20-sided die {103, 203, 1903, 2003}, the mean of the number rolled is .if we relabel the 20-sided die {103, 203, 1903, 2003}, the standard deviation of the number rolled is .