Variants of this silly little cartoon showing a pie chart have been in circulation for some time. Still, this is a nice exercise for elementary school mathematics students to learn about the graphical representation of fractions using pie charts. They can also get some introduction to angles as parts of a circle.
A circular sector is the portion of the disk enclosed by two radii and the included arc of the circle. Since the complete circle encompasses 360, the fraction of the pie eaten or uneaten is equal to the angle of the sector divided by 360. A 90 angle is called a right angle, while 180 is a straight angle.