Using the Angle Sum of a Triangle Worksheet Download
Each problem names two angles of a triangle as equal, gives one measure, and asks which statement about a SUM of two angles must be true. Asking for a sum rather than for a single angle is what makes it a reasoning question: the student has to find the missing angle first and then add. The wrong answers are all numbers the question itself produces by stopping early - the measure that was handed over, the two equal angles added together, the whole 180 degrees of the triangle, and the supplement of the given angle. None is a random number, so none can be ruled out by size alone. Every triangle is drawn to the angles it describes rather than schematically, and the corner numbers sit inside their own corners on the angle bisector so they cannot be read as belonging to a neighbouring vertex.
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