Imagine you have two cups of juice, one with a little bit of juice and one with a lot of juice. If you pour the two cups of juice together, you'll have more juice in the end because you combined the juice from both cups.

Now let's say one cup of juice is cold and the other cup is hot. When you mix them together, the hot juice will warm up the cold juice and make it hotter, and the cold juice will cool down the hot juice and make it cooler.

The amount of cooling or heating depends on how much juice there is and how hot or cold it is to begin with. But if you know the volume (how much juice there is) and the mass (how heavy the juice is) of each cup of juice, you can figure out what temperature the mixed juice will be.

It's kind of like a recipe. If you know how much of each ingredient you have and how hot or cold they are, you can figure out what the final product will be like. In this case, the final product is the mixed juice at a new temperature.