This Exam FM sample reference tests Perpetuity Duration Sensitivity. At 7% the perpetuity-due is worth 152857.14 and has modified duration 13.35113. A 2% yield decline raises the first-order estimate by 40816.33, choice A.
These notes identify the calculation error associated with each wrong letter when that error is reproducible.
BChoice B uses the perpetuity-immediate modified duration 1 divided by 7% rather than the due-perpetuity sensitivity.
CChoice C applies Macaulay duration directly to the 2% yield change.
DChoice D reprices exactly at 5% instead of using the requested first-order approximation.
EChoice E divides the 2% rate change by 7% and applies that proportion directly to price.
Original practice · fully worked
Original variant: estimated gain on an immediate perpetuity
A level perpetuity-immediate pays 500 annually and is valued at 6% effective. The yield immediately falls to 5%. Using first-order modified duration, estimate the dollar increase in value.
A 833.33
B 1,000.00
C 1,250.00
D 1,388.89
E 1,666.67
Variant answer in brief
The initial price is 8333.33 and modified duration is 16.6667. A one-percentage-point decline produces an estimated gain of 1388.89, choice D.
Setup
Setup
Price the immediate perpetuity and compute its modified duration.
P0=0.06500=8,333.333
Dmod=0.061=16.666667
Model
Model
The yield change is negative 0.01.
Δi=0.05−0.06=−0.01
Compute
Compute
Apply the first-order relative price change and convert it to dollars.
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