1.
A body cools from 80 ∘C80\,^\circ\text{C} to 60 ∘C60\,^\circ\text{C} in 5 minutes. The temperature of the surrounding is 20 ∘C20\,^\circ\text{C}. The time it takes to cool from 60 ∘C60\,^\circ\text{C} to 40 ∘C40\,^\circ\text{C} is: