Question

A laptop was purchased for $1,800. Its value is predicted to decay exponentially, decreasing by 20% each year. Which equation can be used to predict
t, the number of years it would take for the laptop to have a value of $900?


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Answer 1

Value each year = 1800*(0.8)^t. Set that equal to 900:
1800(0.8)^t = 900

Divide by 1800:
(0.8)^t = 0.5

So t = log(0.5)/log(0.8) ≈ 3.11 years.