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?

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:

Verification / Alternative check:

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.