College Algebra Name:

Quiz #3
Summer 2000

1. Radioactive strontium-90 is decays exponentially at a continuous rate of approximately 2.27% per year.

a) Express the amount of strontium-90 present as a function of the initial amount A and the number of years t.

b) In 1960, strontium-90 was released into the atmosphere during nuclear weapons testing, and was absorbed into people’s bones. How many years does it take until only 25% of the original amount absorbed remains?

c) One of the main contaminants of the Chernobyl nuclear accident was strontium-90. Preliminary estimates after the Chernobyl disaster suggested that it would take about 100 years before the region would be again safe for human habitation. What percentage of the original strontium-90 would still remain by this time?

2. A potato is placed in a preheated oven to bake. Its temperature P = P(t) is given by

P = 400 - 360(1)^t/40 where p is measured in degrees Fahrenheit and t is the time in minutes since the potato was placed in the oven.

Describe two different methods of finding when the temperature of the potato reaches 270 degrees Fahrenheit and find the exact answer (to within 3 decimal places of accuracy).

3. The following table of data consists of the number of domestic deaths attributes to AIDS from 1981 to 1987 where t is the number of years since 1980 and N is the total number of deaths to that date.

t	1	2	3	4	5	6	7
N	268	1209	3826	8712	17386	29277	41128
y=ln(N)

a) Compute the natural log of each of the values of N and complete the table.

b) Plot y versus t, draw the best fitting line to the data and approximate the equation of the line