Interest and Percentages Made Real
Year 9 Mathematics 60-minute lesson Real-world applications
Lesson Overview
60-minute exploration of percentages in real life Simple interest calculations Percentage increase and decrease Practical applications and problem solving Creative activities and extension challenges
National Curriculum Links
Number: Calculate percentages of amounts Solve problems involving percentage increase and decrease Understand and calculate simple interest Use ratio and proportion in real contexts Apply mathematical skills to practical situations
Learning Objectives
Recall and calculate percentages of quantities Calculate simple interest using the formula I = P × r × t Calculate percentage increase and decrease Apply percentage skills to real-life situations Develop confidence in using percentages
Starter: Percentage Calculation Refresher
Quick-fire questions on mini-whiteboards Calculate: 20% of 150 Calculate: 5% of 80 Calculate: 125% of 40 Work in pairs to support each other
Hook: Simple Interest and Your Money
Imagine you save £100 in a bank account The bank offers 5% interest per year How much money would you have after 1 year? This is called Simple Interest Let's learn the formula to calculate it!
Simple Interest Formula
Simple Interest = P × r × t P = Principal (starting amount) r = Interest rate (as a decimal) t = Time (in years)
Simple Interest: Worked Example
Problem: £200 at 3% for 2 years P = £200 (principal) r = 0.03 (3% as decimal) t = 2 years Interest = 200 × 0.03 × 2 = £12
Your Turn: Simple Interest Practice
Calculate the simple interest: £150 at 4% for 3 years Use your mini-whiteboards Show your working clearly Compare answers with your partner
Percentage Increase
A shop item costs £50, now it's £60 What's the percentage increase? Formula: (Increase ÷ Original Value) × 100 Increase = £60 - £50 = £10 Percentage Increase = (10 ÷ 50) × 100 = 20%
Percentage Decrease
Sale time! Item reduced from £100 to £75 What's the percentage decrease? Formula: (Decrease ÷ Original Value) × 100 Decrease = £100 - £75 = £25 Percentage Decrease = (25 ÷ 100) × 100 = 25%
Real-Life Applications
{"left":"Bank savings accounts earn interest\nSalary increases and bonuses\nInvestment growth over time\nMobile phone contracts with interest","right":"Sale prices in shops\nRestaurant service charges\nInflation affecting prices\nMortgage and loan calculations"}
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