This Exam FM sample reference tests Spot and Forward Rates. Use time 0 as the comparison date. The opening balance and fifteen mid-month charges are borrowing inflows; fifteen month-end payments plus the 3,000 balance treated as an additional payment at month 15 are outflows. The expression with those exponents and fifteen terms is choice E.
These notes identify the calculation error associated with each wrong letter when that error is reproducible.
AChoice A (X +∑ = + ∑) does not satisfy the time-0 balance of fifteen mid-month charges, fifteen month-end payments, and the month-15 ending balance; no distinct standard one-step error is identifiable.
BChoice B (X +∑) does not satisfy the time-0 balance of fifteen mid-month charges, fifteen month-end payments, and the month-15 ending balance; no distinct standard one-step error is identifiable.
CChoice C (X +∑) does not satisfy the time-0 balance of fifteen mid-month charges, fifteen month-end payments, and the month-15 ending balance; no distinct standard one-step error is identifiable.
DChoice D (X +∑) does not satisfy the time-0 balance of fifteen mid-month charges, fifteen month-end payments, and the month-15 ending balance; no distinct standard one-step error is identifiable.
Original practice · fully worked
Original variant: opening credit balance from mid-month charges and month-end payments
A credit account earns 12% annual effective interest. During each of six months, 50 is charged at mid-month and 200 is paid at month-end. Immediately after the sixth payment, the balance is 500. Calculate the balance immediately before the first mid-month charge.
A 1,140.64
B 1,207.74
C 1,274.84
D 1,341.93
E 1,409.03
Variant answer in brief
Discounting six payments and the ending balance, then subtracting the six mid-month charge values, gives opening balance 1,341.93, choice D.
Setup
Setup
Use the monthly accumulation factor equivalent to 12% annual effective.
q=(1.12)1/12
Model
Model
At time 0, opening balance plus charge present values equals payment present values plus the terminal balance present value.
X+n=1∑650q−(n−0.5)=n=1∑6200q−n+500q−6
Compute
Compute
Solving the present-value equation gives X = 1341.93.
X=1341.93239120
Answer
Answer
The opening balance is 1,341.93, selecting choice D.
The 2210-page Financial Mathematics Proof Manual reorganizes 461 verified Exam FM solutions by syllabus skill and adds formula proofs, error patterns, and original worked practice.