This Exam P sample reference tests Uniform Distribution. The unreimbursed amount is min(X,d). For a uniform loss on [0,450], its mean is d-d squared/900. Setting this to 56 gives roots 60 and 840; only 60 lies in the loss support, so choice A.
These notes identify the calculation error associated with each wrong letter when that error is reproducible.
BSubstituting d=87 into the correct limited-mean formula gives 87-87 squared/900=78.59, not 56. This value does not satisfy the required loss partition.
CThe value 112 follows from the shortcut E[min(X,d)] approximately d/2. That treats every retained amount as uniform from zero to d and ignores losses above d that contribute exactly d.
DThe value 169 is approximately three times 56, corresponding to an unsupported d/3 mean approximation. The actual retained distribution has an atom at d.
EKeeping only the below-deductible integral gives d squared/900=56 and d=224.5, near 224. It omits all losses above d, each of which contributes the full deductible to the unreimbursed amount.
Original practice · fully worked
Original variant: retained amount under an increasing loss density
A repair severity X has density f(x)=x/5000 for x between 0 and 100, and zero elsewhere. A service plan applies a deductible of 60 credits, so the customer retains min(X,60). Calculate the expected amount retained by the customer.
A 13.867 credits
B 21.600 credits
C 52.800 credits
D 60.000 credits
E 66.667 credits
Variant answer in brief
The below-deductible contribution is the integral of x squared/5000 from 0 to 60, equal to 14.4. The probability above 60 is 0.64, adding 38.4, so the retained mean is 52.8, choice C.
Setup
Setup
Separate the continuous retained amount below 60 from the capped amount paid by every larger loss.
R=min(X,60)
Model
Model
Compute the probability that the loss crosses the deductible.
FX(x)=∫0x5000udu=10000x2
Pr(X>60)=1−10000602=0.64
Compute
Compute
Add the sub-deductible first moment and the capped contribution.
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