Simple Interest — Principal tripled after 5 years: A sum earns Rs 200 simple interest in the first 5 years. In the next 5 years, the principal is tripled at the same rate. What is the total interest over 10 years?
Aptitude
Simple Interest
Difficulty: Easy
Choose an option
Answer
Correct Answer: ₹ 800
Explanation
Introduction / Context:Under simple interest, interest is proportional to principal, rate, and time. If the principal changes for a subsequent period, the new interest scales linearly with the new principal for that later period.
Given Data / Assumptions:
- First 5 years interest = Rs 200 on principal P at rate r
- After 5 years, principal becomes 3P at the same r
- Next 5 years interest is based on 3P
Concept / Approach:From the first period: P * r * 5 = 200 ⇒ P * r = 40. For the next period: SI = (3P) * r * 5 = 15 * (P * r) = 15 * 40 = 600. Total interest = 200 + 600 = 800.
Step-by-Step Solution:
Compute P * r from first 5 years: 200 / 5 = 40.Next 5 years on 3P: 3 * 5 * (P * r) = 15 * 40 = 600.Total interest = 200 + 600 = Rs 800.Verification / Alternative check:
Proportionality check confirms linear scaling with principal and time under SI.Why Other Options Are Wrong:
- ₹ 650, ₹ 700, ₹ 750, ₹ 850: Do not equal 200 + 3×(200) for equal durations and rate.
Common Pitfalls:
- Treating the process as compound interest.
- Forgetting to triple only for the second 5-year block.
Final Answer:₹ 800.