Solve each word problem by writing an exponential decay function y=a(1-r)^x. These are easier than the ones we did in class, and DO NOT require use of a graphing calculator. A plain calculator can be used. Follow these steps:
1) find the initial value (a)
2) find the rate (r)
3) write the equation and use it to solve the problem
I) Older televisions have electrical parts in them called 'capacitors,' which store large amounts of electricity even after the t.v. has been unplugged from the wall. (This makes them dangerous for the average person to try to repair!) A capacitor starts out with 400 volts of electricity stored in it, but loses 10% of the voltage every hour that the t.v. is unplugged. How many volts are in the capacitor after 5 hours?
II) The temperature of a cup of coffee is 200 degrees Fahrenheit. The cup is losing heat to its surroundings at a rate of 4% every minute. How hot is the coffee after 15 minutes?
III) BONUS: Identify and explain the flaw in the exponential temperature model suggested by problem #II [hint - consider other times that you might want to find the temperature for...]
