This Exam P sample reference tests Expected Value. A high-risk driver has expected annual bonus 48 and a low-risk driver 54. Multiplying by the cohort sizes gives 50,400, choice B.
These notes identify the calculation error associated with each wrong letter when that error is reproducible.
AThe value 48,000 applies the high-risk annual expectation 48 to all 1000 drivers.
CThe value 51,000 applies the unweighted average of annual expectations 48 and 54 to all 1000 drivers, ignoring cohort sizes.
DThe value 54,000 applies the low-risk annual expectation 54 to all 1000 drivers.
EThe value 60,000 pays 5 every month to all 1000 drivers regardless of accident status.
Original practice · fully worked
Original variant: expected annual credits across service tiers
A platform has 800 basic users and 200 premium users. Each month a basic user earns a 3-dollar reliability credit with probability 0.70, while a premium user earns a 5-dollar credit with probability 0.85. Find the expected total credits over 12 months.
A 22,176 dollars
B 24,840 dollars
D 30,360 dollars
C 32,400 dollars
E 36,000 dollars
Variant answer in brief
Monthly expected credits are 800(3)(0.70)+200(5)(0.85)=2,530. Multiplying by 12 gives 30,360 dollars.
Setup
Setup
The monthly expected credit is 2.10 dollars per basic user and 4.25 dollars per premium user.
E[CB]=3(0.70)=2.10
E[CP]=5(0.85)=4.25
Model
Model
Multiply each monthly expectation by its tier population, add the tiers, and then multiply by 12 months.
E[T]=12{800(2.10)+200(4.25)}
Compute
Compute
Basic users contribute 1680 dollars per month and premium users 850, for annual total 12×2530=30,360.
E[T]=12(1680+850)=30360
Answer
Answer
Expected total annual credits are 30,360 dollars, corresponding to choice D.
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