Quadrilaterals

In parallelogram $ABCD$, if $\angle A = (2x - 30)^\circ$ and $\angle C = (x + 20)^\circ$, find $x$.

If a quadrilateral has both pairs of opposite sides equal, then it is a:

In parallelogram $PQRS$, $\angle P = 100^\circ$. What is the measure of $\angle R$?

In a quadrilateral $ABCD$, $\angle A = 40^\circ, \angle B = 140^\circ, \angle C = 40^\circ$, and $\angle D = 140^\circ$. What type of quadrilateral is it?

The diagonals of $ABCD$ are $14\text{ cm}$ and $20\text{ cm}$ long. If they bisect each other, $ABCD$ is a:

A quadrilateral has side lengths $9.1\text{ cm}, 11.2\text{ cm}, 9.1\text{ cm}$, and $11.2\text{ cm}$ respectively. It is a:

In $\triangle ABC$, $P$ and $Q$ are mid-points of $AB$ and $AC$. If $BC = z$, what is the length of $PQ$?

In $\triangle ABC$, $D$ and $E$ are the mid-points of sides $AB$ and $BC$. If $AC = 8.5 \text{ cm}$, find the length of $DE$.

If $x$ is the length of the segment joining the mid-points of two sides of a triangle, and $y$ is the length of the third side, which of the following is true?