Question

find the circumference of the circle whose area is 16 times the area of the circle with diameter 7 cm

Answer 1

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Here is your answer
Let the Radius of big circle is r
So The area of the big circle = πr^2

Diameter of small circle is 7 cm
So Radius of small circle is 7/2 = 3.5 cm
Area of small circle is π(3.5)^2

ATQ
$\pi \times r {}^{2} = 16 \times \pi \times (3.5) {}^{2} \\ {r}^{2} = 16 \times (3.5) {}^{2} \\ r = \sqrt{16 \times (3.5) {}^{2} } \\ r = 4 \times 3.5 \\ r = 14 \: cm$
Now
we know that
Circumference of circle Is
$= 2\pi \times r \\ = 2 \times \frac{22}{7} \times 14 \\ = 2 \times 22 \times 2 \\ = 88 \: cm$
Therefore Circumference of the circle is 88 cm

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Answer 2

Ar of circle=16*22/7*7/2*7/2

Area of circle=616

So

Pie*r square=616

22/7*r*r=616

r*r=196

r=14

Circumference of circle =2*pie*r

=2*22/7*14

=88cm