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问题: 某电台“挑战主持人”节目

解答:

P1(错错错)=(1/5)(1/5)(2/5)=2/125................分值=-10
P2(对错错)=P3(错对错)=(4/5)(1/5)(2/5)=8/125.........=0
P4(对对错)=(4/5)(4/5)(2/5)=32/125...................=10
P5(错错对)=(1/5)(1/5)(3/5)=3/125....................=20
P6(对错对)=P7(错对对)=(4/5)(1/5)(3/5)=12/125........=30
P8(对对对)=(4/5)(4/5)(3/5)=48/125...................=40

过关的概率 = P6+P7+P8 = 72/125 = 57.6%

P(ξ=-10)=P1=2/125
P(ξ=0)=P2+P3=16/125
P(ξ=10)=P4=32/125
P(ξ=20)=P5=3/125
P(ξ=30)=P6+P7=24/125
P(ξ=40)=P8=48/125

数学期望=-10*2/125+0*16/125+10*32/125+20*3/125+30*24/125+40*48/125
    =24分