State whether the following statement is true or false:
The diagonals of a rhombus bisect each other at right angles.

In $\Delta ABC$,$P$ and $Q$ are the midpoints of $AB$ and $AC$ respectively. If $PQ + BC = 8.4 \, cm$ and $AB + AC = 20.5 \, cm$,then find the perimeter of $\Delta ABC$ in $cm$.

Diagonals of a quadrilateral $ABCD$ bisect each other. If $\angle A = 35^{\circ}$,determine $\angle B$. (in $^{\circ}$)

$ABCD$ is a rhombus such that $\angle ACB = 40^{\circ}$. Then $\angle ADB$ is (in $^{\circ}$)

In trapezium $ABCD$,$AB \parallel CD$. If $\angle A = 80^{\circ}$ and $\angle B = 75^{\circ}$,then find $\angle D$. (in $^{\circ}$)

Can all the four angles of a quadrilateral be obtuse angles? Give reason for your answer.