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?

Answer 1

Use exponential decay: 1800(0.8)^t = 900.

Equivalently (0.8)^t = 0.5, so t = ln(0.5)/ln(0.8) ≈ 3.11 years.