Compound Interest — Prelims Strategy

Prelims Strategy

Master the fundamental formula A = P(1 + r/100)^n and its variations for different compounding frequencies. Memorize key relationships like CI - SI difference formulas and effective rate calculations.

Focus on pattern recognition - identify when a word problem involves compound interest principles even if not explicitly stated. Practice mental calculation techniques for common rates (10%, 20%, 25%) and time periods.

Develop shortcuts for quick approximations using binomial expansions for small rates. Pay special attention to reverse calculation problems where principal, rate, or time must be found from given final amounts.

Practice application problems involving population growth, depreciation, and banking scenarios. Common traps include confusing compounding frequencies, calculation errors in exponential terms, and misidentifying simple vs compound interest scenarios.

Use elimination techniques by checking answer reasonableness - compound interest should always exceed simple interest for same parameters after first period. Time management is crucial - allocate maximum 2-3 minutes per compound interest question and use approximation when exact calculation is time-consuming.