Compound Interest – Find principal from 2-year amount at 4%: A sum amounts to ₹ 1,352 in 2 years at 4% compound interest (annual compounding). What was the principal?

Difficulty: Easy

Correct Answer: ₹ 1,250

Explanation:


Introduction / Context:
Finding the original principal from a known future amount over a fixed period at compound interest is a reverse-compounding problem. We divide the amount by the growth factor (1 + r)^t to retrieve the starting principal.



Given Data / Assumptions:

  • A = 1,352
  • r = 4% per annum
  • t = 2 years
  • Annual compounding


Concept / Approach:
Use P = A / (1 + r)^t = 1,352 / (1.04)^2. Calculate the denominator precisely to avoid rounding drift when comparing close options.



Step-by-Step Solution:
(1.04)^2 = 1.0816P = 1,352 / 1.0816 = 1,250



Verification / Alternative check:
Forward check: 1,250 * 1.0816 = 1,352, confirming the principal exactly.



Why Other Options Are Wrong:
₹ 1,200, ₹ 1,260, and ₹ 1,300 fail the exact reverse-compounding equality at 4% over 2 years. ₹ 1,180 is far from the required value.



Common Pitfalls:
Using simple interest to reverse compute principal will not match the compounded outcome; always divide by (1 + r)^t for CI problems.



Final Answer:
₹ 1,250

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