This Exam FM sample reference tests Duration and Convexity. A perpetuity beginning in year 5 has Macaulay duration 15 years at 10%; dividing by 1.10 gives modified duration 13.64, choice A.
These notes identify the calculation error associated with each wrong letter when that error is reproducible.
BChoice B is inconsistent with the deferred-perpetuity duration shift and modified-duration conversion; no distinct standard single-step error producing it is identifiable.
CChoice C is inconsistent with the deferred-perpetuity duration shift and modified-duration conversion; no distinct standard single-step error producing it is identifiable.
DChoice D is inconsistent with the deferred-perpetuity duration shift and modified-duration conversion; no distinct standard single-step error producing it is identifiable.
EChoice E is inconsistent with the deferred-perpetuity duration shift and modified-duration conversion; no distinct standard single-step error producing it is identifiable.
Original practice · fully worked
Original variant: infer when a perpetuity begins
A level annual perpetuity is valued at 8% effective annually. Its modified duration is 18.9815. At the end of which year is its first payment?
A 5
B 6
C 7
D 8
E 9
Variant answer in brief
Modified duration 18.9815 implies Macaulay duration 20.5; subtracting the base perpetuity duration 13.5 gives a seven-year shift, so payment starts in year 8, choice D.
Setup
Setup
Convert the observed modified duration back to Macaulay duration.
DM=(1.08)(18.9815)=20.5
Model
Model
Represent a perpetuity first paid in year k as the ordinary perpetuity duration plus a k-minus-one timing shift.
DM=(k−1)+0.081.08
Compute
Compute
The observed duration exceeds the base 13.5 years by seven years, so k equals eight.
20.5=(k−1)+13.5⟹k=8
Answer
Answer
The first payment occurs at the end of year 8, corresponding to choice D.
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