Ready to skip ahead to practice problems? Click here! Weighted averages have been on my mind, probably because this is the time of year when students are calculating their final course grades! The "usual" average (technically called the ordinary arithmetic mean) is easy enough: Add up all the values you have, divide them by the.

You have a hypothesis - you're excited!  You're sure you're correct and you can't wait to go out there armed with your experiments and prove everyone wrong! But hold up.  Do you know what this emotional response leads to?  Confirmation bias.  Suddenly, all of your results fit your hypothesis!  Every figure you look at is another.