How to Figure out the key of a written music piece

This video is about how to learn how to calculate what key to play a piece of music in. The instructor tells you that you need to know two things: how to read music notes and how understand the Circle of Fifths. Putting together these two layers of knowledge you can figure out what possible keys the music can be in. You can normally narrow down your possibility to two choices. Normally, the key to choose correlates with the last note in the music.