Twenty students take an exam in which the scores are normally distributed with mean 75 and variance 64. An A is a score of 90-100, a B is 80-90, a C is 70-80, a D is 60-70 and an F is any score below 60. Let Y₁ be the number of students that get an A on the exam, Y₂ the number of students that get a B, Y₃ the number of students that get a C, Y₄ the number of students that get a D and Y₅ the number of students that get an F.

Find (a) p(3, 6, 8, 2, 1), (b) E[Y₁], (c) V (Y₂) and (d) Cov(Y₃, Y₄).