More Calorimetry?

Question

A 100 g sample of water at 90 degrees C is added to a 500 g sample of water at 10 degrees C. what is the final temperature?

Answer 1

This method is called the "weighted average":

total amount of water is 600 grams

1/6th of it (100/600) is at 90 C
5/6ths of is (500/600) is at 10 C

(1/6 * 90) + (5/6 * 10) = ??? (you can do the numbers, easy)