Algebra 2 Pre AP
PS: More Growth and Decay
1) Which of the exponential functions below show growth and which show decay?
a)
y  5(2) x
b)
y  100(.5) x
c)
y  80(1.3) x
d)
y  20(0.8) x
e)
y  20(1  0.025) x
f)
y  40(1  0.4) x
2) Since January 1980, the population of the city of Brownville has grown according to the mathematical
model
y  720,500(1.022) x , where x is the number of years since January 1980.
a) Explain what the numbers 720,500 and 1.022 represent in this model.
b) What would the population be in 2000 if the growth continues at the same rate? Round to nearest whole number.
(1,113,402)
c) Use this model to predict about when the population of Brownville will first reach 2,000,000? (2027)
3) A population of 800 beetles is growing each month at a rate of 5%.
a) Write an equation that expresses the number of beetles at time x.
b) About how many beetles will there be in 8 months? Round to nearest beetle.(1182)
4) The half-life of a medication is the amount of time for half of the drug to be eliminated from the body.
The half-life of Advil or ibuprofen is represented by the
equation
R  M (0.5)
t
2
, where R is the amount of Advil remaining in the
body, M is the initial dosage, and t is time in hours.
a) A 200 milligram dosage of Advil is taken at 1:00 pm. How many milligrams
of the
medication will remain in the body at 6:00 pm? Round to 3 decimal places. (35.355mg)
b) If a 200 milligram dosage of Advil is taken how many milligrams of the medication will
remain in the body 12 hours later? Round to 3 decimal places (0.049mg)
5) Your new computer cost $1500 but it depreciates in value by about 18% each year.
a) Write an equation that would indicate the value of the computer at x years.
b) How much will your computer be worth in 6 years? (456.01)
6)
You drink a beverage with 270 mg of caffeine. Each hour, the caffeine in your system decreases by
about 28%. How much caffeine will you have in your system 4 hours later? (72.56mg)
7)
Your baby brother has an ear infection. The doctor said there are probably 50,000,000 bacteria in
his left ear. The penicillin the doctor prescribed will kill 7% of the bacteria every 6 hours. How many
bacteria will be in your brother’s ear in . . .
a) 1 day (37402600.5)
b) 5 days (11711943.68)
c) 3 hours (48218253.8)
8)
A car is originally valued at $30,000. Each year the car is worth 80% of the previous year’s
value. In approximately how many years will the car be worth ¼ of its original cost? (6-7)
9)
A graph goes through the point (1,2) and (2,8).
a. If the relationship is linear, what would be the equation of the line in slope-intercept form?
b. If the relationship was exponential, what would be the equation of the curve in y=abx form?
10)
Solve a.
2x-5=3x+6
b. x2+9x=-14
c. x3-64=0
d. 2m+3(42m)=8m-2