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If the diameter of a circle increases by 50 percent, by what percent

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If the diameter of a circle increases by 50 percent, by what percent  [#permalink]

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New post 10 Jan 2019, 03:27
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A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

68% (01:09) correct 32% (01:12) wrong based on 35 sessions

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Re: If the diameter of a circle increases by 50 percent, by what percent  [#permalink]

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New post 10 Jan 2019, 03:57
My answer D
If the diameter increases 50%, the radius also increases 50%.
The area would remain Pi(r^2)
Say for example Radius increases from 10 to 15
the area would increase from 100pi to 225pi.
therefore 125% increase.
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Re: If the diameter of a circle increases by 50 percent, by what percent  [#permalink]

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New post 10 Jan 2019, 06:06
Bunuel wrote:
If the diameter of a circle increases by 50 percent, by what percent will the area of the circle increase?

A. 25%
B. 50%
C. 100%
D. 125%
E. 225%


radius = 2 dia 4
area = 4pi
50% increase in dia = 4*1.5 = 6
radius = 3
area = 9pi
% change in area = 9pi-4Pi/ 4 pi = 125 % IMO D
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If the diameter of a circle increases by 50 percent, by what percent  [#permalink]

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New post 10 Jan 2019, 07:32

Solution


Given:
    • The diameter of a circle increases by 50%

To find:
    • The percentage increase in area of the circle

Approach and Working:
Let ‘d‘ be the initial diameter
    • Area = \(ᴨ\frac{d^2}{4}\) = A

New diameter = \(d + \frac{d}{2} = \frac{3d}{2}\)
    • Area = \(ᴨ(\frac{3d}{2})^2/4 = 9ᴨ\frac{d^2}{16} = \frac{9A}{4}\)

Percentage increase in area = \([(\frac{9A}{4} – A)/A] *100 = 125\)%

Hence, the correct answer is Option D

Answer: D

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If the diameter of a circle increases by 50 percent, by what percent   [#permalink] 10 Jan 2019, 07:32
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