Lesson 55: Simple Interest & Real Life

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• Lesson Description
• Learning Objectives
• Topics Covered
• Key Terms
• Lesson Examples
• Practice Problems
• Tips & Common Mistakes
• Summary
• Challenge Problems
• Unit Navigation

Lesson Description

This lesson introduces simple interest, a fundamental concept in finance, and teaches how to apply the formula I = P × R × T (Interest = Principal × Rate × Time) to solve real-life problems involving loans, savings, and investments.

Learning Objectives

• Understand the formula for simple interest.
• Calculate interest earned or owed for a given principal, rate, and time.
• Apply simple interest to real-life scenarios, such as loans and savings.

Topics Covered

• Simple interest formula: I = P × R × T
• Calculating interest for different time periods
• Applications to loans, savings, and real-world finance

Key Terms

• Principal (P): The initial amount of money borrowed or invested.
• Rate (R): The annual interest rate as a decimal or percentage.
• Time (T): The time the money is borrowed or invested, usually in years.
• Simple Interest (I): The extra money earned or paid, calculated as P × R × T.

Lesson Examples

Example 1: Calculating Simple Interest

1. A loan of $5000 is taken at 6% simple interest per year for 3 years.
2. Interest: I = P × R × T = 5000 × 0.06 × 3
3. I = $900. Total repayment = 5000 + 900 = $5900

Example 2: Savings Account

1. $2000 is invested at 4% simple interest for 5 years.
2. Interest: I = 2000 × 0.04 × 5 = $400
3. Total amount after 5 years: 2000 + 400 = $2400

Practice Problems

1. A person invests $1500 at 5% simple interest for 4 years. Calculate the interest earned.
2. Find the total amount to repay for a $2500 loan at 7% simple interest over 2 years.
3. If $1200 is invested at 3% for 6 years, what is the total interest earned?
4. A loan of $800 at 6% simple interest is repaid after 1.5 years. Calculate the interest.

Tips & Common Mistakes

• Always convert the interest rate to decimal before calculating (e.g., 5% → 0.05).
• Ensure the time period matches the rate period (years vs months).
• Remember that simple interest does not compound.

Summary

Simple interest is a straightforward method for calculating interest on loans or investments. Understanding it helps in making informed financial decisions and solving practical money-related problems.

Challenge Problems

1. An investment of $5000 earns 6% simple interest for 7 years. Find the total interest earned.
2. A person borrows $2000 at 8% simple interest for 3.5 years. How much interest is owed?
3. If a bank offers $1000 at 5% simple interest per year, how long will it take to earn $250 interest?