### Eliminating Long Calculations
In IBPS PO and SSC CGL Tier 1 exams, time per question is capped at 42 seconds. Solving compound interest problems using `A = P(1 + r/100)^n` leads to severe time exhaustion.
### The Effective Percentage Rate Method
- For 2 years at 10% per annum: Effective CI rate = `10 + 10 + (10*10)/100 = 21%`.
- For 2 years at 5% per annum: Effective CI rate = `5 + 5 + 0.25 = 10.25%`.
Directly compute the principal with this multiplier to bypass compound fraction expansions.