Profit, Loss and Interest

Overview

Profit, Loss and Interest forms a core quantitative topic in TN TET Mathematics, appearing consistently in both Paper I and Paper II. This topic tests your ability to apply percentage concepts to real-world commercial transactions—buying and selling goods, lending and borrowing money. Mastery here builds the foundation for teaching students how mathematics connects to everyday life, from shopkeepers calculating margins to banks computing loan repayments.

For TN TET, expect 2–4 questions from this area. Problems typically involve straightforward calculations of profit/loss percentages, finding cost or selling price, and computing simple or compound interest for given periods. The pedagogy angle also matters—you should understand how to teach these concepts using real-life examples and help students avoid common calculation errors.

Success requires memorising key formulas, understanding their derivations, and practising quick mental calculations since exam time is limited.

Key Concepts

• **Cost Price (CP)** is the amount paid to acquire an item; **Selling Price (SP)** is the amount received when selling it. The relationship between these determines profit or loss.

• **Profit occurs when SP > CP**; the gain equals SP − CP. **Loss occurs when SP < CP**; the loss equals CP − SP.

• **Profit and Loss percentages are always calculated on Cost Price**, not Selling Price—this is the standard convention unless stated otherwise.