Pg 329

Exponential Decay How would you show 15% decay?

Identify the initial amount a and the decay factor b in each exponential function. y = 8 · 0.8x f (x) = 12 · 0.1x

Exponential Decay Word Problems More Practice

Example 5 The half life of a radioactive substance is the length of time it takes for half of the substance to decay into another substance. Radioactive iodine is used to treat some forms of cancer. The half life of iodine-131 is 8 days. A patient receives a 12mCi (millicuries) treatment. How much iodine 131 is left in the patient 16 days later? 16 days = 2 half lives a = ? b = ? x = ?

Example 6 In 1980, the population of a town was 17,000. The population has been decreasing at a rate of 1.4% per year. At that rate, what will the population of the town be in 1990? a = ? b = ? x = ?

Example 7 The half-life of a certain substance is 4 days. If you have 100 g of the substance, how much will be left after 12 days?

Example 8 The value of a $1750 computer decreases 30% annually. What will be the value of the computer after 3 years?