Question 22.

On a rectangular metal sheet of area 135 sq in, a circle is painted such that the circle touches opposite two sides. If the area of the sheet left unpainted is two-thirds of the painted area then the perimeter of the rectangle in inches is

A
3√π(5 + 12π\frac{12}{π} )
B
4√π(3 + 12π\frac{12}{π} )
C
5√π(3 + 12π\frac{12}{π} )
D
3√π(52\frac{5}{2} + 6π\frac{6}{π} )
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Question Explanation

Text Explanation

Total area = 5 parts


Let ABCD be the rectangle with length 2l2l and breadth 2b2b respectively.

Area of the circle i.e. area of painted region =πb2= \pi b^{2}.

Given, 4lbπb2=23πb24lb - \pi b^{2} = \frac{2}{3}\pi b^{2}.

4lb=53πb2\Rightarrow 4lb = \frac{5}{3}\pi b^{2}.

l=5π12b\Rightarrow l = \frac{5\pi}{12} b.

Given, 4lb=1354lb = 135  

45π12b2=135\Rightarrow 4 \cdot \frac{5\pi}{12} b^{2} = 135  

b=9π\Rightarrow b = \frac{9}{\sqrt{\pi}}.

l=154π\Rightarrow l = \frac{15}{4}\sqrt{\pi}.

Perimeter of rectangle =4(l+b)= 4(l + b)  

=4(154π+9π)= 4\left( \frac{15}{4}\sqrt{\pi} + \frac{9}{\sqrt{\pi}} \right)  

=3π(5+12π)= 3\sqrt{\pi}\left(5 + \frac{12}{\pi}\right).

Hence option A is correct.

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