Question

Which figure is a counterexample to the following statement? A quadrilateral with one pair of parallel sides is a parallelogram.

Answer 1

Answer: Trapezoid

A trapezoid is a quadrilateral with exactly one pair of parallel sides. The other two opposite sides are not parallel. In order to have a parallelogram, we need two pairs of opposite parallel sides (not just one pair). Since a trapezoid is not a parallelogram, this means this is a counterexample to the original statement.