1. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Warm Up Simplify each expression. 1. (4 + 0.05) 2 3. 4. The first term of a geometric sequence is 3 and the common ratio is 2. What is the 5th term of the sequence? 5. The function f(x) = 2(4) x models an insect population after x days. What is the population after 3 days? 26.5302 1.0075 2. 25(1 + 0.02) 3 16.4025 48 128 insects

2. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Solve problems involving exponential growth and decay. Objective

3. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay

4. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Example 1: Exponential Growth The original value of a painting is $9,000 and the value increases by 7% each year. Write an exponential growth function to model this situation. Then find the painting’s value in 15 years. Step 1 Write the exponential growth function for this situation. y = a(1 + r) t = 9000(1 + 0.07) t = 9000(1.07) t Substitute 9000 for a and 0.07 for r. Simplify. Write the formula.

5. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Example 1 Continued Step 2 Find the value in 15 years. y = 9000(1.07) t = 9000(1 + 0.07) 15 ≈ 24,831.28 The value of the painting in 15 years is $24,831.28. Substitute 15 for t. Use a calculator and round to the nearest hundredth. The original value of a painting is $9,000 and the value increases by 7% each year. Write an exponential growth function to model this situation. Then find the painting’s value in 15 years.

6. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Example 2 A sculpture is increasing in value at a rate of 8% per year, and its value in 2000 was $1200. Write an exponential growth function to model this situation. Then find the sculpture’s value in 2006. Step 1 Write the exponential growth function for this situation. y = a(1 + r) t = 1200(1.08) t Write the formula Substitute 1200 for a and 0.08 for r. Simplify. = 1200(1 + 0.08) 6

7. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Example 2 Continued A sculpture is increasing in value at a rate of 8% per year, and its value in 2000 was $1200. Write an exponential growth function to model this situation. Then find the sculpture’s value in 2006. Step 2 Find the value in 6 years. y = 1200(1.08) t = 1200(1 + 0.08) 6 ≈ 1,904.25 The value of the painting in 6 years is $1,904.25. Substitute 6 for t. Use a calculator and round to the nearest hundredth.

8. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay

9. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Example 3: Exponential Decay The population of a town is decreasing at a rate of 3% per year. In 2000 there were 1700 people. Write an exponential decay function to model this situation. Then find the population in 2012. Step 1 Write the exponential decay function for this situation. y = a(1 – r) t = 1700(1 – 0.03) t = 1700(0.97) t Write the formula. Substitute 1700 for a and 0.03 for r. Simplify.

10. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Example 3: Exponential Decay Continued The population of a town is decreasing at a rate of 3% per year. In 2000 there were 1700 people. Write an exponential decay function to model this situation. Then find the population in 2012. Step 2 Find the population in 2012. ≈ 1180 Substitute 12 for t. y = 1,700(0.97) 12 Use a calculator and round to the nearest whole number. The population in 2012 will be approximately 1180 people.

11. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay The fish population in a local stream is decreasing at a rate of 3% per year. The original population was 48,000. Write an exponential decay function to model this situation. Then find the population after 7 years. Step 1 Write the exponential decay function for this situation. y = a(1 – r) t = 48,000(1 – 0.03) t = 48,000(0.97) t Write the formula. Substitute 48,000 for a and 0.03 for r. Simplify. Example 4

12. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Step 2 Find the population in 7 years. ≈ 38,783 Substitute 7 for t. y = 48,000(0.97) 7 Use a calculator and round to the nearest whole number. The population after 7 years will be approximately 38,783 people. The fish population in a local stream is decreasing at a rate of 3% per year. The original population was 48,000. Write an exponential decay function to model this situation. Then find the population after 7 years. Example 4 Continued

13. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay A common application of exponential decay is half-life. The half-life of a substance is the time it takes for one-half of the substance to decay into another substance.

14. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Example 5: Science Application Astatine-218 has a half-life of 2 seconds. Find the amount left from a 500 gram sample of astatine-218 after 10 seconds. Step 1 Find t, the number of half-lives in the given time period. Divide the time period by the half-life. The value of t is 5. Write the formula. = 500(0.5) 5 Substitute 500 for P and 5 for t. = 15.625 Use a calculator. There are 15.625 grams of Astatine-218 remaining after 10 seconds. Step 2 A = P(0.5) t

15. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Example 6: Science Application Astatine-218 has a half-life of 2 seconds. Find the amount left from a 500-gram sample of astatine-218 after 1 minute. Step 1 Find t, the number of half-lives in the given time period. Divide the time period by the half-life. The value of t is 30. 1(60) = 60 Find the number of seconds in 1 minute.

16. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Example 6 Continued Astatine-218 has a half-life of 2 seconds. Find the amount left from a 500-gram sample of astatine-218 after 1 minute. Step 2 A = P(0.5) t Write the formula. = 500(0.5) 30 Substitute 500 for P and 30 for t. = 0.00000047 Use a calculator. There are 0.00000047 grams of Astatine-218 remaining after 60 seconds.

17. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Example 7 Cesium-137 has a half-life of 30 years. Find the amount of cesium-137 left from a 100 milligram sample after 180 years. Step 1 Find t, the number of half-lives in the given time period. Divide the time period by the half-life. The value of t is 6.

18. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Example 7 Continued Cesium-137 has a half-life of 30 years. Find the amount of cesium-137 left from a 100 milligram sample after 180 years. Step 2 A = P(0.5) t Write the formula. = 100(0.5) 6 Use a calculator. There are 1.5625 milligrams of Cesium-137 remaining after 180 years. Substitute 100 for P and 6 for t. = 1.5625

19. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Bismuth-210 has a half-life of 5 days. Find the amount of bismuth-210 left from a 100-gram sample after 5 weeks. (Hint: Change 5 weeks to days.) Step 1 Find t, the number of half-lives in the given time period. Divide the time period by the half-life. The value of t is 7. Example 8 5 weeks = 35 days Find the number of days in 5 weeks.

20. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Bismuth-210 has a half-life of 5 days. Find the amount of bismuth-210 left from a 100-gram sample after 5 weeks. (Hint: Change 5 weeks to days.) Example 8 Continued Step 2 A = P(0.5) t Write the formula. = 100(0.5) 7 = 0.78125 Use a calculator. There are 0.78125 grams of Bismuth-210 remaining after 5 weeks. Substitute 100 for P and 7 for t.

21. Holt McDougal Algebra 1 9-3 Exponential Growth and Decay Homework Read Section 9-3 in the workbook Workbook page 521: 1 – 9