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What is the circumference of a circle whose area is 49π?

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What is the circumference of a circle whose area is 49π?  [#permalink]

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New post 17 Jan 2019, 04:48
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A
B
C
D
E

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What is the circumference of a circle whose area is 49π?

A 7π
B 14π
C 24.5π
D 35π
E 49π
Spoiler: OA

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Re: What is the circumference of a circle whose area is 49π?  [#permalink]

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New post 17 Jan 2019, 05:07
Bunuel wrote:
What is the circumference of a circle whose area is 49π?

A 7π
B 14π
C 24.5π
D 35π
E 49π


Area = 49 π
π r^2 = 49 π
r = 7

C = 2π7
C =14 π

Answer B
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Re: What is the circumference of a circle whose area is 49π?  [#permalink]

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New post 17 Jan 2019, 06:35

Solution


Given:
    • Area of the circle = 49ᴨ

To find:
    • The circumference of the circle

Approach and Working:
Area = \(ᴨr^2 = 49ᴨ\)
    • Implies, \(r^2 = 49\)
    • Thus, r = 7

Circumference = 2ᴨr = 2ᴨ * 7 = 14ᴨ

Hence, the correct answer is Option B

Answer: B

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Re: What is the circumference of a circle whose area is 49π?  [#permalink]

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New post 19 Jan 2019, 19:23
Finding area from circumference seems to be asked frequently, so it can't hurt to learn the formula

\(Area = \frac{C^2}{(4π)}\)

We are given that A=49π

\(49π = \frac{C^2}{(4π)}\)
\(49π·4π = C^2\)
\(7^2·2^2·π^2=C^2\)
\(7·2·π=C=14π\)
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Re: What is the circumference of a circle whose area is 49π?  [#permalink]

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New post 20 Jan 2019, 02:54
Bunuel wrote:
What is the circumference of a circle whose area is 49π?

A 7π
B 14π
C 24.5π
D 35π
E 49π

\(πr^2 = 49π\)

So, \(r = 7\)

Thus, the circumference will be \(2*π*7 = 14π\) , Answer must be (B) 14π
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Re: What is the circumference of a circle whose area is 49π?   [#permalink] 20 Jan 2019, 02:54
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