Proportion, Profit, Loss, Interest and Currency Exchange | Form 2 Mathematics

Proportion, Profit, Loss, Interest and Currency Exchange

Commercial arithmetic applies ratio and percentage ideas to prices, investments and exchange rates.

Core formulas

• Profit = selling price − cost price; loss = cost price − selling price.
• Profit percentage = profit ÷ cost price × 100%; loss percentage is defined similarly.
• Simple interest I = PRT/100, where R is the percentage rate and T is time in years.
• Amount with compound interest A = P(1 + R/100)ᵀ.

Worked examples

1. A book bought for 2,000 FCFA and sold for 2,400 FCFA gives profit 400 FCFA and profit percentage 20%.
2. For P = 50,000 FCFA, R = 6% and T = 2 years, simple interest is 50,000 × 6 × 2 / 100 = 6,000 FCFA.
3. At 1 EUR = 655 FCFA, 10 EUR = 6,550 FCFA.

Practice

1. Find the loss percentage when an item costing 8,000 FCFA is sold for 7,200 FCFA.
2. Find simple interest on 120,000 FCFA at 5% for 3 years.
3. Convert 75 USD to FCFA using a stated exchange rate.