Simple Interest – Find rate percent from two amounts: A sum amounts to Rs 1,260 in 2 years and to Rs 1,350 in 5 years at simple interest. Find the annual rate of interest (percent per annum).

Introduction / Context:
Two amounts at two times under SI directly reveal the uniform annual interest, enabling calculation of both principal and rate. Here, only the rate is asked.

Given Data / Assumptions:

• A2 = Rs 1260 (t = 2 years)
• A5 = Rs 1350 (t = 5 years)

Concept / Approach:
Annual SI = (A5 - A2) / (5 - 2). Principal P = A2 - 2 * (annual SI). Rate r% = (annual SI / P) * 100.

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

• 30% / 10% / 5% / 7.5%: do not fit the computed annual increase and principal.

Common Pitfalls:

• Dividing by total time instead of the time gap between the two amounts.
• Using compound interest logic.

Final Answer:
2.5% per annum.