# Pre Calc Checkup 4

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Pre Calc Checkup 4
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Checkup: Applications of Logarithms
Answer the following questions using what you 've learned from this lesson. Write your responses in the space provided, and turn the assignment in to your instructor.

For 1 – 2, use the following situation:

In 1991, the cost of mailing a 1 oz. first-class letter was 29 cents, and the inflation rate was 4.6%. If the inflation rate stayed constant, the function C(t) = .29(1.046)t would represent the cost of mailing a first-class letter as a function of years since 1991.

1. If the function given holds true, in what year would the cost of mailing a first-class letter reach 60 cents?

The cost of mailing a first-class letter would reach 60 cents in 2007.

2. In 2007, the cost of mailing a first-class letter was 41 cents. Has the inflation rate stayed constant since 1991? Explain.

No the inflation rate has not remained constant because in 1991 the cost of mailing a first-class letter was 29 cents, causing the inflation rate to be 4.6%. If this rate were to be constant until 2007, the cost would be 60 cents instead of 41 cents.

For 3 – 5, use the following situation:

A hot bowl of soup cools according to Newton’s law of cooling. Its temperature (in degrees Fahrenheit) at time t is given by T(t) = 68 + 144e-.04t, where t is given in minutes.

3. What was the initial temperature of the soup?

212 degrees Fahrenheit

4. What is the temperature of the soup after 15 minutes?

147.03 degrees Fahrenheit

5. How long after serving is the soup 125F?

23 minutes

6. A forensic detective is called to the scene of a murder at 2 a.m. When she checks the temperature of the body, she finds that it is 80F. The temperature of the room in which the body is found is 65F.

If the detective uses Newton’s law of cooling, T(t) = TA + (T0 - TA))e-0.1947t, what will she say was the time of death?

10p.m

7. An archeologist finds an artifact that contains 44% of the carbon-14 that it would have

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