Download 5.8 Exponential Growth and Decay

January 30, 2012
5.8 Exponential Growth and Decay
January 30, 2012
1. Iodine 131 is a radioactive material that decays according to the function
where A 0 is the initial amount present at time t (in days). Assume that a
scientist has a sample of 100 grams of iodine 131.
(a) What is the decay rate of iodine 131?
(b) How much iodine 131 is left after 9 days?
(c) When will 70 grams of iodine 131 be left?
(d) What is the half–life of iodine 131?
January 30, 2012
2. A culture of bacteria obeys the law of uninhibited growth.
(a) If N is the number of bacteria in the culture and t is the time in hours, express
(b) If 500 bacteria are present initially and there are 800 after one hour,
how many will be present in the culture after 5 hours?
(c) How long is it until there are 20,000 bacteria?