A circle of radius $7 c m$ is scaled $3$ times. Then the perimeter of the circle become:

3

times the original perimeter

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6

times the original perimeter

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9

times the original perimeter

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Doesn't change

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Solution

The correct option is A $3$ times the original perimeter
Radius of circle $= 7 c m$
Perimeter $= 2 π r = 2 \times π \times 7 = 14 π c m$
When scaled $3$ times
New radius $= 3 \times 7 = 21 c m$
New Perimeter $= 2 π r = 2 \times π \times 21 = 42 π c m$
Ratio of perimeters $= \frac{42 π}{14 π} = 3$
So the perimeter becomes three times.

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A circle of radius 7 cm is scaled 3 times. Then the perimeter of the circle become:

The correct option is A 3 times the original perimeterRadius of circle =7 cmPerimeter =2πr=2×π×7=14π cmWhen scaled 3 timesNew radius =3×7=21 cmNew Perimeter =2πr=2×π×21=42π cmRatio of perimeters =42π14π=3So the perimeter becomes three times.

A circle of radius $7 c m$ is scaled $3$ times. Then the perimeter of the circle become: