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Q.

If the area of a circle, whose radius is 5 cm is increased to four times, then find the changed radius?


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a

10 cm

b

12 cm

c

8 cm

d

14 cm 

answer is A.

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Detailed Solution

Given, the area of a circle 5 cm.
We need to find the changed radius when area is increased 4 times.
Use formula for area of circle and substitute radius R = 5 cm.
Area of the circle = πr²
= π × (5)²
= 25π cm²
Area is increased 4 times, so multiply area by 4 and
4 × 25π = πr²
100 = πr²
100 = r
The radius of the circle is 10 cm.
Hence, the correct option is 1.
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