5. Two samovars - a large one and a small one - were filled with very hot water of the same temperature. Both samovars have the same shape and are made of the same material. Which one will cool down to room temperature first?
Answer: smaller. Solution. If one samovar is $n$ times larger than the other, then its volume is larger by $n^{3}$ times, and the surface area is larger by $n^{2}$ times. Therefore, in the larger samovar, there is $n$ times more volume per unit of surface area. Thus, it will cool down more slowly.