Let H denote the number of times Harry Potter manages to irritate Professor Snape in one day. Let R denote the number of times Ron Weasley manages to irritate Professor Snape in one day. Let the joint probability density function for (H, R) be h+r -24- 0 he(1,2), re(0, 1, 2, 3} otherwise uh, r)=
(a) Calculate Cov[H, R].
(b) Each day, Professor Snape takes 20 points from Gryffindor, simply because he can. Additionally, Professor Snape takes 10 points from Gryffindor each time Ron Weasley irritates him. The only person that Snap