All possible values of ξ are 0, 1, 2.
P(ξ=0)=C246C250=207245，P(ξ= 1)= c 146 c 14c 250 = 184 1225，P(ξ
Therefore, the distribution list of ξ is
(2) According to the histogram of frequency distribution, the number of excellent and poor students in Class A is 65,438+02,38 respectively, and the number of excellent and poor students in Class B is 4,46 respectively.
According to the data in the contingency table:
K2= 100×( 12×46？ 4×38)2 16×84×50×50≈4.762
Because the score is 4.762 > 3.84 1, there is a 95% assurance that "excellent grades" are related to teaching methods.