Simple Interest – Find the principal from two amounts: A sum amounts to Rs 850 in 3 years and Rs 925 in 4 years at simple interest. Find the principal (original sum).

Introduction / Context:
The per-year increase under SI equals the difference between consecutive-year amounts. Subtracting the appropriate multiple from an earlier amount reveals the principal.

Given Data / Assumptions:

• A3 = Rs 850
• A4 = Rs 925

Concept / Approach:
Annual SI = A4 - A3. Then P = A3 - 3 * (annual SI).

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

• Rs 600 / 575 / 650: not consistent with both amounts.
• Data inadequate: data is sufficient in SI.

Common Pitfalls:

• Mistaking SI for compound interest.

Final Answer:
Rs 625.