Music is Math

Music is just simple math. Whenever we add a dot to a note, it adds on half the value of the note.
You already know that a half note gets two beats. The dot adds half the value on top of the original note value. Half of 2 is 1 and 2 plus 1 is 3. So a dotted half note gets 3 beats. You knew that grade school math would pay off someday!