Mixing different temperatures of water ?

[Dmitri10]

"What would be the final temperature if you mixed a liter of 20 degrees C water with 2 liters of 40 degrees C water?"

My teacher assigned us several problems like these without bothering to explain them. I have a hunch that they are embarrassingly simple to complete, but I know not how to find the solutions. The only equation we've been given to this point is Q = mcΔT.

ANY help would be appreciated. Thanks in advance.

 

[Dick]

Q is the heat energy. The amount of heat coming out of the hotter water is equal to the amount of heat going into the cooler water. Suppose the final temperature is T (somewhere between 20 and 40 degrees). Find the change in heat for each mass of water and equate them. Then solve for T.