A liquid takes 5 minute to cool from $ 80 ^\circ C to 50 ^\circ C$ . The temperature of the surrounding is $ 20 ^\circ C$ . What is the time it will take to cool from $ 60 ^\circ C to 30 ^\circ C$ ?
Using the equation $ { \theta_1 - \theta _2 \over t } = K \left( {\theta_1 + \theta_2 \over 2} - \theta_0 \right) \theta_0$ = where = temperature of surrounding