Principal trebled midway — total simple interest over 10 years: The simple interest on a sum of money is ₹ 600 after 10 years. If the principal is tripled after 5 years (rate unchanged), what is the total simple interest at the end of 10 years?

Introduction / Context:When principal changes partway through an investment under simple interest, compute interest separately for each phase and add them. The given single-amount interest helps deduce P * r first.

Given Data / Assumptions:

• Total SI over 10 years on the original setup = ₹ 600
• Principal is tripled after 5 years
• Rate r is unchanged
• We seek total SI over the entire 10-year period under the changed scenario

Concept / Approach:From I = P * r * t / 100, if I10 = ₹ 600 for 10 years at (P, r), then P * r = 600 * 100 / 10 = 6000. Use this to compute phase-wise interest with principal P for 5 years and 3P for the next 5 years.

Step-by-Step Solution:P * r = 6000Interest for first 5 years: I1 = (P * r * 5) / 100 = 6000 * 5 / 100 = ₹ 300Interest for last 5 years with 3P: I2 = (3P * r * 5) / 100 = 3 * 6000 * 5 / 100 = ₹ 900Total interest = I1 + I2 = 300 + 900 = ₹ 1200

Verification / Alternative check:This linear approach is valid for SI because interest depends independently on each phase’s principal and time, then sums up.

Why Other Options Are Wrong:₹ 600 and ₹ 900 ignore the tripling effect; “Data inadequate” is incorrect because P * r is deducible from the given 10-year total SI.

Common Pitfalls:Confusing total 10-year SI across scenarios or mistakenly compounding (this is SI, not CI).

Final Answer:₹ 1200