Final answer:
The third angle in the triangle is 20 degrees, which is found by subtracting the sum of the given two angles (120 degrees and 40 degrees) from the total sum of angles in any triangle, which is 180 degrees.
Step-by-step explanation:
The measure of the third angle in a triangle can be determined using the fact that the sum of all three angles in a triangle is always 180 degrees. Given that the first two angles are 120 degrees and 40 degrees, you can find the third angle by subtracting the sum of these two angles from 180 degrees.
So, the calculation would be 180 degrees - 120 degrees - 40 degrees = 20 degrees.
Therefore, the measure of the third angle in the triangle is 20 degrees.