If a wire is bent into the shape of a square,then the area of the square is $81 \, cm^2$. When the wire is bent into a semi-circular shape,the area of the semi-circle will be (in $cm^2$):

What is the area of the shaded portion if each side of the square measures $21\,cm$? (in $cm^2$)

The perimeter of a square is equal to twice the perimeter of a rectangle whose dimensions are: length $8 \, cm$ and breadth $7 \, cm$. What is the circumference of a semicircle whose diameter is equal to the side of the square? (in $cm$) (Rounded off to two decimal places)

If the length and breadth of a rectangular plot are increased by $50 \%$ and $20 \%$ respectively,then the new area is how many times the original area?

$A$ wire is looped in the form of a circle of radius $28\, cm$. It is bent again into a square form. What will be the length of the diagonal of the largest square possible thus?

If the radius of a circle is reduced by $40 \%$,then its circumference is reduced by (in $\%$).