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Q.

A wire when bent in the form of a square encloses an area of 992.25 cm 2  . If the same wire is bent in the form of a semicircle, what will be the radius of the semicircle so formed?


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a

24.5

b

45.2

c

42.2

d

45.5 

answer is A.

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Detailed Solution

We need to find the radius of the semicircle obtained. It is given that the wire used to create the semicircle was bent in the form of a square with an area 992.25 cm 2  .
Area= a 2  
IMG_256
We know that the given area is 992.25 cm 2  .Hence,
a 2 =992.25  
a= 992.25 =31.5 cm  
Let us find the perimeter of the square,
Perimeter=4a  
Perimeter=4×31.5=126 cm  
It is given that the same wire is used to form a semicircle. Hence,
Perimeter of the square = circumference of the semicircle…(i)  
We know that the circumference of a semicircle with radius r is given as
Circumference=πr+2r  
Let us substitute this in (i). We will get
πr+2r=126  
r(π+2)=126  
r( 22 7 +2)=126  
r 36 7 =126  
r=126× 7 36  
r=24.5 cm  
Hence, the radius of the semicircle is 24.5 cm.
 
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