Simple Interest — Tiered rates over 12 years: Anil borrows at simple interest: 5% p.a. for the first 3 years, 8% p.a. for the next 2 years, 10% p.a. for the next 4 years, and 12% p.a. for the final 3 years. If total interest over 12 years is Rs 8560, find the principal.

Introduction / Context:
Aggregating simple interest across multiple fixed-rate intervals is additive. Summing the block contributions yields a single multiplier times principal equal to total interest paid.

Given Data / Assumptions:

• Years 1–3: 5% ⇒ 0.05 * 3 = 0.15
• Years 4–5: 8% ⇒ 0.08 * 2 = 0.16
• Years 6–9: 10% ⇒ 0.10 * 4 = 0.40
• Years 10–12: 12% ⇒ 0.12 * 3 = 0.36
• Total SI = Rs 8560 (12 years)

Concept / Approach:
Total SI factor = 0.15 + 0.16 + 0.40 + 0.36 = 1.07; hence 1.07 * P = 8560 ⇒ P = 8560 / 1.07.

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

• 6000, 5000, 7000, 9000 do not satisfy 1.07 * P = 8560.

Common Pitfalls:

• Forgetting the last 3-year block at 12%.

Final Answer:
Rs 8000.