124HW12solutions

# 124HW12solutions - Math 124 Homework 12(section 2.4...

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Math 124 Homework 12 (section 2.4), solutions to graded problems 2) The temperature, T , in degrees Fahrenheit, of a cold yam placed in a hot oven is given by T = f ( t ), where t is the time in minutes since the yam was put in the oven. (a) What is the sign of f ( t )? Why? (b) What are the units of f (20)? What is the practical meaning of the statement f (20) = 2? Solutions: (a) f ( t ) is positive since the yam is increasing in temperature in the oven. (b) The units of f (20) are in degrees Fahrenheit per minute . The practical meaning of f (20) = 2 is this: After 20 minutes, the temp. of the yam is increasing at a rate of 2 degrees Fahrenheit per minute. 6) Suppose C ( r ) is the total cost of paying off a car loan borrowed at an annual interest rate of r %. What are the units of C ( r )? What is the practical meaning of C ( r )? What is its sign? Solution: The units are dollars per percent . The practical meaning of C ( r ) is this: C ( r ) is approximately the additional cost of taking out a loan when 1 more interest percent is charged, when r is the current interest rate. The sign of

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