(Ⅰ) ? Excellent or not? Total A 104555B203050? The total is 3075105 (Ⅱ) k2 =105× (10× 30-20× 45) 255× 50× 30× 75 = 6.109;

(3) Assuming that "the grade has nothing to do with the class",

K2=6. 109>5.024，P(k2>5.024)≈0.025

There is a 97.5% certainty that "grades are related to classes."