Original practice · fully worked
Original variant: capped reimbursement among eligible invoices
A maintenance invoice X is uniformly distributed from 0 to 15 thousand dollars. A service fund reimburses 60% of the portion above 3 thousand dollars, subject to a maximum reimbursement of 6 thousand dollars. Given that an invoice produces a positive reimbursement, find the probability that the reimbursement reaches its maximum.
- A
0.1333 - B
0.1667 - C
0.2500 - D
0.5000 - E
0.8333
Answer and calculation
A positive reimbursement requires X>3, while the cap is reached once 0.6(X-3) is at least 6, or X at least 13. The conditional uniform length ratio is 2/12=1/6, choice B.
Setup
Setup
Translate positivity and the capped-payment event into invoice thresholds.
{Y>0}={X>3} {Y=6}={0.6(X−3)≥6} Model
Model
Solve the cap inequality within the uniform support.
0.6(X−3)≥6⟺X≥13 Compute
Compute
Condition by dividing the cap interval length by the positive-payment interval length.
Pr(Y=6∣Y>0)=15−315−13 Pr(Y=6∣Y>0)=61=0.1666667 Answer
Answer
One sixth of eligible invoices reach the reimbursement cap.
0.1667(B)