Question 78710
A top-quality fax-copying machine is purchased for $5800.  After t years its value is given by the exponential function V(t)=5800(.8)to the power of t .

The company decides to replace the machine when its value declined to $500.  After how long will the machine be replaced?
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EQUATION:
500=5800(0.8)^t
Divide by 5800 to get:
5/58 = (0.8)^t
Take the log of both sides:
-1.064457 = tlog(0.8)
-1.064457 = t(-0.09691)
t=10.9839 yrs
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Cheers,
Stan H.