AM-77

Exponential and logarithmic models

A Math · Secondary 3 · Hard · Exponential and logarithmic models

A liquid cools according to the model

\theta = 20 + 60e^{-0.05t}

, where

\theta

is the temperature in

^\circ\text{C}

and

t

is the time in minutes after it is removed from a heater.

Find the time taken for the liquid to cool to

40^\circ\text{C}

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