Question

关于初学概率论习题

请问这道题怎么写步骤，有点看不懂。题1.7

Answer 1

设f(x)为某人击中x弹的概率
f(x)=C(4,x)*((3/5)^x)*((1-3/5)^(4-x))
f(0)=(1-3/5)^4=16/625
f(1)=4*(3/5)*(1-3/5)^3=96/625
f(2)=6*(3/5)^2*(1-3/5)^2=216/625
f(3)=4*(3/5)^3*(1-3/5)=216/625
f(4)=(3/5)^4=81/625
分数期望值
=0*f(0)+15*f(1)+30*f(2)+55*f(3)+100*f(4)
=44.64