Simple Interest – Rate to triple the principal: At what annual simple interest rate will a sum of money become three times the principal in 25 years?

Introduction / Context:
Tripling under SI means the interest equals 2P over the period. The linear relation SI = P * r * t lets us directly solve for r.

Given Data / Assumptions:

• Target amount = 3P
• Time t = 25 years
• Simple interest model

Concept / Approach:
If A = 3P, then SI = A - P = 2P. Therefore P * r * t = 2P → r = 2 / t.

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

• 5% / 6% / 7.5% / 12%: do not satisfy r = 2 / 25.

Common Pitfalls:

• Interpreting tripling as interest = 3P (it is 2P).

Final Answer:
8% per annum.