This Exam FM sample reference tests Interest Credited over a Specified Year. Under force 1/(t+1), the first account grows from 9 at time 2 to 12 at time 3, earning 3 during the third year. The corresponding bank-account interest factor is 0.055125, giving X = 54.42 and choice E.
These notes identify the calculation error associated with each wrong letter when that error is reproducible.
AChoice A equates 3 to one year of 5% interest on X, ignoring that the third-year base has already grown for two years.
BChoice B uses the first account's time-3 balance 12 rather than its third-year interest of 3.
CChoice C compares total three-year interest in the two accounts instead of interest earned only in year 3.
DChoice D uses the bank's second-year interest increment rather than the third-year increment.
Original practice · fully worked
Original variant: match second-year interest under two models
A deposit of 5 is placed in a fund with force of interest 2 divided by t plus 2. Another deposit X earns 4% effective annually. Find X so that the interest earned during the second year, from time 1 to time 2, is the same in both accounts.
A 168.27
B 192.31
C 200.00
D 210.34
E 218.75
Variant answer in brief
The force-based account earns 8.75 during year 2. Dividing by 1.04 squared minus 1.04 gives X = 210.34, choice D.
Setup
Setup
Integrating 2/(t+2) makes the first balance proportional to (t+2) squared.
A(t)=5(2t+2)2
Model
Model
Compute its increase from time 1 to time 2.
A(2)−A(1)=5(22−1.52)=8.75
Compute
Compute
Set this equal to second-year interest in the 4% account.
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