This Exam P sample reference tests Expected Value. The limited policy has expected payment 284/75, while the ordinary-deductible policy has expected payment 72/25. Their absolute difference is 68/75=0.906667, which rounds to 0.91 and choice D.
These notes identify the calculation error associated with each wrong letter when that error is reproducible.
AThe value 0.32 is twice F_X(4)=0.16. It manipulates the probability of a sublimit loss instead of integrating the two payment amounts.
BThe value 0.64 is 4F_X(4). It assigns the limit to losses below four and omits the actual payments above four, so it is not either expected payment or their difference.
CThe value 0.79 results from rounding the deductible-plan expectation 2.88 to 3 before subtracting it from 3.7867. The expected payments must retain precision until the final difference.
EThe value 1.12 is 4-2.88. It assumes the limited policy always pays its maximum 4, even though losses below four receive their actual smaller amounts.
Original practice · fully worked
Original variant: expected reimbursement from a three-part support rule
A repair cost X, measured in thousands, equals 2, 7, or 12 with probabilities 0.22, 0.51, and 0.27. A support contract reimburses 60% of the first 6, plus 30% of any amount above 6. It also adds 1.5 when the cost exceeds 10. Calculate the expected reimbursement.
A 0.405
B 0.639
C 3.072
D 3.975
E 4.116
Variant answer in brief
The three possible reimbursements are 1.2, 3.9, and 6.9. Weighting them by probabilities 0.22, 0.51, and 0.27 gives an expected reimbursement of 4.116, which is choice E.
Setup
Setup
Express the three-part reimbursement as one payment function.
R(x)=0.6min(x,6)+0.3(x−6)++1.5I(x>10)
Model
Model
Evaluate the payment function at each possible repair cost.
R(2)=1.2,R(7)=3.6+0.3=3.9
R(12)=3.6+1.8+1.5=6.9
Compute
Compute
Weight the three reimbursements by the cost probabilities.
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