Applications 11: Exponential and Logarithmic Equations

1. Finance

Sung Lee invests $5,000 at age 18. He hopes the investments will be worth

$10,000 when he turns 25. If the interest is compounded continuously,

approximately what rate of growth will he need to achieve his goal? Is that a

reasonable expectation? Why or why not?

2. Sound

The formula for measuring sound intensity in decibels D is defined by the

1D = 10log(+),

where I is the intensity of the sound, in watts per

-12 W

square meter, and I = 10

is the lowest level of sound that the average

person can hear. What is the intensity of a hair dryer that makes a sound of

90dB?

equation

m