Loan Amortization under Compound Interest — Three equal end-of-year payments: A man borrows ₹ 4000 at 7 1/2% p.a. compound interest. At the end of every year he pays ₹ 1500 (covering interest and part principal). How much does he still owe after three such payments?

Difficulty: Medium

Correct Answer: Rs. 123.25

Explanation:


Introduction / Context:
This is a straightforward amortization with annual compounding: each year the outstanding balance accrues interest, then the borrower pays a fixed amount, reducing the balance. Repeating the process year by year yields the remaining debt after the specified number of payments.



Given Data / Assumptions:

  • Initial principal P0 = ₹ 4000
  • Annual interest rate i = 7.5% = 0.075
  • End-of-year payment each year = ₹ 1500
  • Number of payments = 3


Concept / Approach:
Iterate: after interest, subtract the payment. Algebraically: B1 = P0(1 + i) − 1500; B2 = B1(1 + i) − 1500; B3 = B2(1 + i) − 1500. The remaining balance after the 3rd payment is owed to the bank.



Step-by-Step Solution:

After year 1: 4000 * 1.075 = 4300; pay 1500 ⇒ B1 = 2800.After year 2: 2800 * 1.075 = 3010; pay 1500 ⇒ B2 = 1510.After year 3: 1510 * 1.075 = 1623.25; pay 1500 ⇒ B3 = ₹ 123.25.


Verification / Alternative check:

Annuity-present-value equivalence gives the same residual when reversed; iterative method is clearer here.


Why Other Options Are Wrong:

  • ₹ 125 and ₹ 469.18 are near-miss computations typically arising from rounding or misordering “interest then payment”.
  • ₹ 400 and ₹ 0 do not reflect the calculated amortization path.


Common Pitfalls:

  • Subtracting the payment before applying interest; the problem states end-of-year payments (interest applies first).


Final Answer:
Rs. 123.25.

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