A if you add 2 ounces of 40f cream to the 180f coffee

(a) If you add 2 ounces of 40°F cream to the 180°F coffee in the cup, how long will it take for the
mixture to reach drinking temperature? Give your answer (in minutes) in decimal form with at least 3
decimal digits (for example, 12.345 minutes).
16.033 16.03261 minutes
(b) If you let the 12 ounces of 180°F coffee cool for 5 minutes before adding 2 ounces of 40°F cream,
how long will it take (after the initial time when the coffee was 180°F) for the mixture to reach drinking
temperature? Give your answer (in minutes) in decimal form with at least 3 decimal digits (for example,
12.345 minutes).
15.760 15.75983 minutes
(c) In order to reach drinking temperature as quickly as possible, should you add the cream
immediately, or wait 5 minutes?
you should add the cream immediately
you should wait 5 minutes

11/17/14, 2:19 PM Math 125 HW_9C
Page 8 of 8
7. 9/9 points | Previous Answers
A person borrows $10,000 and repays the loan at the rate of $2,400 per year. The lender charges
interest of 10% per year. Assuming the payments are made continuously and interest is compounded
continuously (a pretty good approximation to reality for long-term loans), the amount M ( t ) of money (in
dollars) owed t years after the loan is made satisfies the differential equation
and the initial condition
(a) Solve this initial-value problem for M ( t ).
M ( t ) =
(b) How long does it take to pay off the loan? That is, at what time t is M ( t ) = 0? Give your answer (in
years) in decimal form with at least 3 decimal digits.
5.390 5.389965 years
= M − 2400
dM
dt
1
10
M (0) = 10000.