Pre-test and review for test on logarithms and exponents tomorrow.

4. Find
Find

6. Sugar is put into a large quantity of water and the mixture is stirred. After 2
minutes 50% of the sugar has dissolved. How much longer will it take until 90%
of the sugar has dissolved? (Model the sugar dissolving as an exponential decay
function.)

8. A $12 000 car depreciates exponentially, losing each year 8% of the value it
had at the begining of the year. What is the value of the car 6 years and 3
months after its purchase?

10. What is the domain of

12. The half life of Iodine-131, a radionuclide used in diagnosing thyroid
disease, is 8 days.
(a) If the X-ray department of the Grace Hospital has 1000 mg of
Iodine-131, write the amount of Iodine-131 remaining after t days.
(b) How many days must pass before the Iodine-131 drops to a level of
100 mg?

13. The decibal (dB) is used to measure
the loudness of sound. Barely audible
sound has a decibal level of 0 and an
intensity level of 10-12 W/m2 (watts
per square meter). Sound painful to the
ear has a decibal level of 130 and an
intensity of 10 W/m2. The formula
gives the decibal level of a sound whose intensity is I; I0 is the intensity
of barely audible sound. Some decibal levels and intensities are shown
in the table below; the intensity is given in watts per square meter.
(a) The intensity of thunder is 1012 times the intensity of barey audible sound.
What is the decibal level of thunder?
(b) If the decibal levels of a subway train entering a station and normal
conversation are 100 dB and 60 dB, respectively, how many times as intense as
normal conversation is the noise of the subway train?
ANSWER: 10 000 times

14. At the begining of an experiment a colony of flibberdejibbets has 2 million
members. After 4 hours the population has increased by 20%. At that time a
biologist, Dr. Trapper John, treats the colony with an agent that slows the
colony’s rate of growth. At the new growth rate, the colony takes three times as
long to double in size as at the old growth rate. How long after the treatment
with the size of the colony of flibberdejibbets reach 12 million?
ANSWER: 106 hours