To find the ratio of the mass of cold water to hot water required, we can use the principle of heat transfer. The heat lost by the hot water is equal to the heat gained by the cold water.
We can use the equation:
(mass of hot water) x (temperature difference) = (mass of cold water) x (temperature difference)
Let's assume the mass of hot water is H and the mass of cold water is C. The temperature difference between the hot water and the desired temperature is 65°C - 45°C = 20°C. The temperature difference between the cold water and the desired temperature is 45°C - 30°C = 15°C.
Using the equation, we have:
H x 20 = C x 15
To find the ratio, we can divide both sides of the equation by H:
20 = (C/H) x 15
Therefore, the ratio of the mass of cold water to hot water required is 15/20, which simplifies to 3/4.