Exercise
May 13'23
Answer
Key: A
[[math]]\begin{aligned}
B & =\left\{\begin{array}{cc}
c(400-x) & x\lt400 \\
0 & x \geq 400
\end{array}\right. \\
100 & =\operatorname{E}(B)=c 400-c \operatorname{E}(X \wedge 400) \\
& =c 400-c 300\left(1-\frac{300}{300+400}\right) \\
& =c\left(400-300 \frac{4}{7}\right) \\
c & =\frac{100}{228.6}=0.44
\end{aligned}[[/math]]