Exponential Growth and Decay Objectives Determine the multiplier

Exponential Growth and Decay Objectives: • Determine the multiplier for exponential growth and decay • Write and evaluate exponential expressions to model growth and decay situations

Modeling Bacteria Growth Time (hr) 0 Population 25 1 2 3 4 5 6 50 100 200 400 800 1600 Write an algebraic expression that represents the population of bacteria after n hours. The expression is called an exponential expression because the exponent, n is a variable and the base, 2, is a fixed number. The base of an exponential expression is commonly referred to as the multiplier.

Example 1 Find the multiplier for each rate of exponential growth or decay. a) 9% growth 100% + 9% = 109% = 1. 09 b) 0. 08% growth 100% + 0. 08% = 100. 08% = 1. 0008 c) 2% decay 100% - 2% = 98% = 0. 98 d) 8. 2% decay 100% - 8. 2% = 91. 8% = 0. 918

Example 2 Suppose that you invested $1000 in a company’s stock at the end of 1999 and that the value of the stock increased at a rate of about 15% per year. Predict the value of the stock, to the nearest cent, at the end of the years 2004 and 2009. Since the value of the stock is increasing at a rate of 15%, the multiplier will be 115%, or 1. 15 = $2011. 36 = $4045. 56

Example 3 Suppose that you buy a car for $15, 000 and that its value decreases at a rate of about 8% per year. Predict the value of the car after 4 years and after 7 years. Since the value of the car is decreasing at a rate of 8%, the multiplier will be 92%, or 0. 92 = $10, 745. 89 = $8, 367. 70

Practice A vitamin is eliminated from the bloodstream at a rate of about 20% per hour. The vitamin reaches a peak level in the bloodstream of 300 mg. Predict the amount, to the nearest tenth of a milligram, of the vitamin remaining 2 hours after the peak level and 7 hours after the peak level.