This document discusses compound interest, which is interest calculated on both the principal amount and accumulated interest over time. Compounding makes a significant difference in the final investment amount. Examples are provided to demonstrate compound interest calculations using the compound interest formula. The rule of 72 is also explained as a way to estimate doubling time for investments based on the interest rate. Students complete activities to practice applying compound interest calculations.

1. Consumer Math 30S Unit 1 – Income & Debt Compound Interest

2. Compound Interest An investment earns compound interest when the interest from each time period is added to the principal and earns interest in subsequent time periods. Because the principal grows, the interest earned grows as well. Compounding makes a significant difference in the final amount an investment is worth. Although compounding interest earns you more money when you are investing, compounding interest costs you more when you borrow. Unit 1 – Income & Debt Outcome 1-2: Use simple and compound interest calculations to solve problems

3. Compound Interest Unit 1 – Income & Debt Outcome 1-1: Solve problems involving performance based income

5. Compound Interest A = P(1 + ) A total amount, including principal and interest P the amount of principal, loan, or deposit r rate expressed as a decimal n the number of compounding periods per year t time in years What affect will there be on the total amount (A) if . . . . . . the amount of time is increased? . . . the number of compounding periods doubled? r n nt Unit 1 – Income & Debt Outcome 1-2: Use simple and compound interest calculations to solve problems

6. Example Problem: Monica wants to invest $1000 at 7½% for 3 years compounded quarterly. What will be the total value of her investment at the end. Unit 1 – Income & Debt Outcome 1-2: Use simple and compound interest calculations to solve problems

8. Example Problem: How long does it take for an investment to double if the rate is 12%? Unit 1 – Income & Debt Outcome 1-2: Use simple and compound interest calculations to solve problems

9. Compound Interest Activity Step 1 Each student roles a die 4 times and records the numbers rolled. Step 2 Repeat Step 1 three more times to have a total of 4 trials. Step 3 Determine the compound interest formula for each trial as outlined below. Unit 1 – Income & Debt Outcome 1-2: Use simple and compound interest calculations to solve problems

10. Compound Interest Activity - continued Step 4 Write down your 4 formulas on the board. Step 5 Look at all formulas and predict which one will result in the most amount of money (A). Step 6 Determine the total amount A for your own 4 formulas. Unit 1 – Income & Debt Outcome 1-2: Use simple and compound interest calculations to solve problems

11. Unit 1 – Income & Debt Outcome 1-2: Use simple and compound interest calculations to solve problems

12. Textbook Assignment: Page 38 - 39 Questions 1 - 10 Unit 1 – Income & Debt Outcome 1-2: Use simple and compound interest calculations to solve problems

13. Compound Interest Review Worksheet Questions 1 - 9 Unit 1 – Income & Debt Outcome 1-2: Use simple and compound interest calculations to solve problems