Original practice · fully worked
Original variant: infer a segment rate from the portfolio average
Forty percent of a portfolio consists of newly issued contracts, whose event rate is 0.12. The remaining contracts are seasoned. The whole portfolio has event rate 0.18. Determine the event rate among seasoned contracts.
- A
0.120 - B
0.180 - C
0.220 - D
0.240 - E
0.300
Answer and calculation
The portfolio rate is a two-segment weighted average. Solving 0.18=0.40(0.12)+0.60s gives s=0.22, choice C.
Setup
Setup
Let s be the event rate among seasoned contracts; the new and seasoned portfolio shares are 0.40 and 0.60.
s=Pr(E∣seasoned) Model
Model
Express the overall event rate as the weighted average of the two segment-specific rates.
0.18=0.40(0.12)+0.60s Compute
Compute
The new-contract contribution is 0.40(0.12)=0.048, leaving 0.132 for seasoned contracts; division by 0.60 gives s=0.22.
0.132=0.60s,s=0.22 Answer
Answer
The seasoned-contract event rate is 0.220, so the correct answer is choice C.
0.22(C)