A triangle has 3 sides and 3 angles. The sum of the measures of the angles is 180 degrees. If you know the measure of two of the angles, you can find the measure of the third angle by following 2 steps. The first step is to add the measures of the the 2 angles. The second step is to subtract that sum from 180 degrees.
To find the third angle of a triangle when you know the measures of two angles are 20° and 40°. The first step is to add, 20° + 40° = 60°. The second step is to subtract this sum from the total, 180° - 60° = 120°. The measure of the third angle is 120°.
In each problem of this problem set you will be given the measures of 2 angles of a triangle. You are to calculate the measure of the 3rd angle. Strive to accomplish these steps with ease and then strive for speed. Good luck and enjoy the challenge!