Math Exponential Growth and Decay

Honors Pre-Calculus Exponential Growth and Decay 3.5 D1 Worksheet Name__________________________________ Exponential Growth: Exponential Decay: Compound Interest: Compound Interest Continuously: 1. 2. The value in dollars of a car years from now is ( ) ( ). a. What is the annual rate of depreciation, the rate at which the car loses value? b. In how many years will the value of the car be approximately half what it is now? The value of a car in dollars years from now is ( ) ( ). a. What is the annual rate of depreciation (the rate at which the car loses value?) b. In how many years will the value of the car be approximately what it is now? 3. The value of a new car decreases each year. The value ( ) of the car is in dollars and its age is in years. In how many years will the value of the car be approximately one-fourth of what it is now? 4. The cost of a certain brand of camera has been increasing at find the cost: a. 5. years and months from now b. The value of a computer depreciates at the rate of find its approximate value: a. years and months from now b. per year. If a camera now costs , years and months ago per year. If a computer is now worth months ago , 6. Complete the table below. The cost of each item grows exponentially. Item Annual Rate of Increase Cost Now Cost in a. Airplane Ticket b. Jar of Mustard c. College Tuition 7. years Cost in years Complete the table below. The value of each item decays exponentially. Item Annual Rate of Decrease Cost Now Value in a. Farm Tractor b. Value of the Dollar c. Value of the Dollar is invested so that it grows at the rate of years? years Value in years 8. If per year, what will the investment be worth in 9. Suppose you invest $500 at 6% annual interest. Calculate the amount you would have after one year if the interest is compounded as follows: a. quarterly b. monthly c. daily d. continuously EFFECTIVE ANNUAL YIELD: 10. Find the effective annual yield for each answer in #9. a. b. c. d. e. Why are these four answers greater than the original interest rate in #9? 11. One hundred dollars deposited in a bank that compounds interest quarterly yields $107.50 over 1 year. a. Find the annual interest rate b. Find the effective annual yield 12. After a year during which interest is compounded quarterly, an investment of $800 is worth $851. What is the effective annual yield? 13. With which plan would an investor earn more, Plan A or Plan B Plan A: A 6% annual rate compounded annually over a 10-year period Plan B: A 5.5% annual rate compounded quarterly over a 10-year period 14. With which plan would an investor earn more, Plan A or Plan B Plan A: A 8% annual rate compounded quarterly over a 5-year period Plan B: A 7.5% annual rate compounded daily over a 5-year period 15. Suppose that $1000 is invested at 7% interest compounded continuously. How much money would be in the bank after 5 years? 16. Suppose $5000 is compounded continuously, and in 10 years, you have $5665.74. a. What is the annual percentage rate? 17. b. How long does it take to for the $5000 to double at that rate? Suppose $7500 takes 21 years to double when compounded continuously. a. What is the annual percentage rate? b. How much will be in the account after 10 years? 18. You invest $2400 in a certificate of deposit (CD) that compounds interest monthly at a rate of 2.25%. How long will it take the $2400 to grow to $3200, if no deposits or withdrawals are made? 19. A sum of $1000 is invested at an interest rate of 4.1% per year. Find the time required for the amount to grow to $4000 if interest is compounded continuously. 20. Find the time required for an investment of $5000 to grow to $8000 at an interest rate of 7.5% per year, compounded quarterly. 21. A sum of $1000 is invested for four years, and the interest is compounded semiannually. If this sum amounted to $1435.77 in the given time, what was the interest rate? 22. A sum of $2000 is invested at an interest rate of 3.25% per year. Find the time for the money to double if the interest is compounded according to the following method. a. semiannually b. monthly c. continuously RULE OF 72 23. Use the Rule of 72 to estimate how long a $2000 investment, invested at a rate of 3.25%, would take to double? Why is this amount more than the answers in #22? 24. Suppose that $1000 is invested at 8% interest compounded annually. How long would it take for the investment to double? 25. Suppose that $2050 is invested at 6% interest compounded monthly. How long would it take for the investment to double? 26. Suppose that $3200 is invested at 2.5% interest compounded monthly. How long would it take for the investment to double? Answers 1a. 15% 1b. 4.27 years 2a. 21% 2b. 5.11 years 4a. $181.82 4b. $108.15 5a. $876.85 5b. $3876.52 6a. $1213.67, $4909.96 6b. $1.97, $3.87 6c. $31124.91, $80730.00 7a. $27421.88, $11568.60 7b. $0.83, $0.69 7c. $0.78, $0.61 8. $6727.50 9a. $530.68 9b. $530.84 9c. $530.92 10a. 6.136% 10b. 6.168% 10c. 6.184% 10d. 6.184% 10e. These are the actual rates that were applied, based on the frequency by which the $500 was compounded 11a. 7.3% 11b. 7.5% 12. 6.375% 13. Plan A 14. Plan A 15. $1419.07 16a. 1.25% 16b. 55.45 years 17a. 3.3% 17b. $10432.26 18. 12.8 years 19. 33.8 years 20. 6.33 years 21. 9.25% 22a. 21.5 years 22b. 21.4 years 22c. 21.3 years 23. 22.2 years; Because of the frequency with which the $2000 investment is compounded. The Rule of 72 is an estimate – the more often the money is actually compounded, the faster it will reach the doubled amount. 24. 9 years 25. 12 years 26. 28.8 years 3. 9d. 6.21 years $530.92