Original practice · fully worked
Original variant: expected Pareto excess above a threshold
A load X has density f(x)=3/x⁴ for x at least 1. A relief contract pays the amount by which X exceeds 2. Find the expected payment.
- A
0.0625 - B
0.1000 - C
0.2000 - D
0.2500 - E
0.1250
Answer and calculation
The Pareto survival function is x⁻³. Integrating that tail beyond two gives expected excess 1/8=0.125, choice E.
Setup
Setup
Integrating the Pareto-type density gives a survival function equal to the inverse cube of the threshold.
S(x)=x−3,x≥1 Model
Model
The expected excess above two is the integral of that survival function from two to infinity.
E[(X−2)+]=∫2∞S(x)dx Compute
Compute
The tail integral equals one eighth, or 0.125.
E[(X−2)+]=∫2∞x−3dx=81 Answer
Answer
The expected excess payment is 0.125, selecting choice E.
0.125(E)