This is a short lesson I use with my Year 8 students as a reminder of how to find the interior sum of a polygon, and thus how to find the value of one angle. It is not an in depth lesson exploring where the formula comes from, although it is referred to in the lesson. There are many 'hidden' calculations and diagrams that can be revealed during the lesson. These are identified as light dots, but are not noticeable when the hidden info is revealed. The lesson finishes with a more advanced example of how angles sums are used to solve problems.