This could be called a lesson on COMPARING PARTS TO THE TOTAL IN A PROPORTION: 2:3:4 Those three numbers in that proportion add up to 9. The three angles of the triangle we want add up to 180², Notice this: 2 isths of the total of 9. 3 is ths of the total of 9. 4 is ths of the total of 9. Similarly, since the angles of a triangle add up to 180°, we want to know: 1. WHAT is ths of the total of 180°? 2. WHAT is ths (or ) of that total of 180°? 3. WHAT is ths of the total of 180°? The answer to the first one, "WHAT is ths of the total of 180°?" is found simply by multiplying by that fraction ·180° = 40°. So that's one of the angles. The other two angles are found the same way. You'll get 60° and 80° for them. It checks because they add up to 180°. Edwin