(1)由题设知ξ=0,1,2,3,4,
P(ξ=0)=[10/20]=[1/2],
P(ξ=1)=[1/20],
P(ξ=2)=[2/20]=[1/10],
P(ξ=3)=[3/20],
P(ξ=4)=[4/20]=[1/5],
∴ξ的分布列为:
ξ 0 1 2 3 4
P [1/2] [1/20] [1/10] [3/20] [1/5]…(3分)
∴Eξ=0×
1
2+1×
1
20+2×
1
10+3×
3
20+4×
1
5=1.5.…(4分)
Dξ=(0−1.5)2×
1
2+(1−1.5)2×
1
20+(2−1.5)2×
1
10+(3−1.5)2×
3
20+(4−1.5)2×
1
5=2.75.…(6分)
(2)由η=a2Dξ,得a2×2.75=44,即a=±4,…(8分)
又Eη=aEξ+b,
∴当a=4时,由2=4×1.5+b,得b=-4;
当a=-4时,由2=-4×1.5+b,得b=8.
∴