X = 6...(6 points)
(2) According to the stem leaf diagram, among the five girls, there are 3 excellent and 2 not.
According to the title, ξ=2, 3, 4,
p(ξ= 2)= c 12c 1 1c 15c 14 = 1 10，
P(ξ=4)=C 12C23C35=35，
P(ξ= 3)= 1-P(ξ= 2)-P(ξ= 4)= 3 10，
The list of ∴ξdistribution is:
ξ2 3 4p 1 10 3 10 6 10eξ= 2× 10+3×3 10+4×6 10 = 72 ...