easiest method - measure the temperature mixture water by any suitable thermometer.Suppose, began to fill the tub or other container, you let too much hot water.Then, discovering his mistake, you immediately cut off valve hot water and added some cold.How to determine the final temperature ?Stir the water and use any suitable thermometer (eg medical).
You can also calculate the resulting temperature mixture advance.Suppose you have a volume V1 hot water with a temperature t1.To it surged some cold water with the volume V2 and the temperature t2.We need to calculate what the final temperature t will have mixture .Heat loss to the environment is negligible.
and heat capacity, and density water of different temperatures is the same.Consequently, the final temperature will depend on the volume ratio.One can easily understand that in any case the final temperature t is intermediate between t1 and t2, but less than the value V2 compared to V1, the closer to the t is t1, and vice versa.
Final temperature t is calculated by the following formula: t = (t1V1 + t2V2) / (V1 + V2).Substituting into this formula known to you the value of temperature and volume, and performing calculations, you define the desired temperature mixture water .
Of course, your task would be completely solved in the same way, if instead of the volume you have to know the mass of water m1 and m2.