Simple and Compound Interest — Study Notes
Overview
Simple and Compound Interest is a high-scoring topic in SOF IMO that connects everyday banking and finance with mathematical computation. Students must master the formulas for SI and CI, understand the difference between them, and solve multi-step word problems involving principal, rate, time, and amount. This topic frequently appears in the Everyday Mathematics section and occasionally in the Achievers Section when combined with other concepts like profit-loss or time-work.
The key challenge is not just applying formulas but interpreting real-world scenarios: loans, deposits, recurring payments, and instalment schemes. Problems may involve finding any unknown variable (principal, rate, time, or amount), comparing SI and CI on the same sum, or breaking down payments into instalments. Strong arithmetic and algebraic manipulation skills are essential.
Expect 2–4 questions directly on this topic in the exam, with marks ranging from straightforward one-step calculations to multi-layered HOTS problems worth 3–4 marks each.
Key Concepts
- **Simple Interest (SI)** is calculated only on the original principal for the entire period. The interest earned each year remains constant.
- **Compound Interest (CI)** is calculated on the principal plus accumulated interest from previous periods. Money "grows on itself," leading to exponential growth.