Physics
posted by Jen .
"Luke Skywalker mixes 250g of hot water (75 deg C) with 500g of cool water (15 deg C). What is the final temperature of the water?"
If someone could just give me a formula, I'd be fine. :)

heat lost by hot water + heat gained by cold water = 0
mass H2O x specific heat water x delta T + (mass H2O x specific heat water x delta T) = 0
For delta T in each case substitute Tf  Ti (for Tf = final T and Ti = initial T). You will have only one unknown, namely Tf. Solve for that.