Grade 5

Suggest that students sketch possibilities on paper or dry erase boards. Emphasize that they may estimate the angle measurements, taking care to notice whether the angles are acute, obtuse, or right.

None of the other angles in the quadrilateral ABCD are larger than angle B. Angle A and angle C are congruent, and angle D is a right angle. What can you say?

- Quadrilateral ABCD could be a rectangle; then all of the angles would be 90
^{o.} - Angle B cannot be acute, because if it was, then angle D will be larger than it.
- If angle B is a right angle, ABCD has to be a rectangle.
- If angle B measures 110
^{o}, then angle B and angle D together measure 200^{o}, and angle A and angle C have to measure 80^{o}each so that the total for all four angles is 360^{o}. This is how ABCD could look.

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