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# If the diameter of circle A is eight times that of circle B, what is

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Math Expert
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If the diameter of circle A is eight times that of circle B, what is  [#permalink]

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30 Oct 2018, 01:37
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25% (medium)

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68% (00:46) correct 32% (00:42) wrong based on 59 sessions

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If the diameter of circle A is eight times that of circle B, what is the ratio of the area of circle A to the area of circle B?

A. 4:1
B. 8:1
C. 16:1
D. 32:1
E. 64:1

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If the diameter of circle A is eight times that of circle B, what is  [#permalink]

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30 Oct 2018, 02:10
Bunuel wrote:
If the diameter of circle A is eight times that of circle B, what is the ratio of the area of circle A to the area of circle B?

A. 4:1
B. 8:1
C. 16:1
D. 32:1
E. 64:1

$$\frac{D_A}{D_B} = \frac{8}{1}$$

Ratio of Areas $$= (\frac{D_A}{D_B})^2$$

i.e. $$\frac{Area of A}{Area of B} = (\frac{8}{1})^2 =\frac{64}{1}$$

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If the diameter of circle A is eight times that of circle B, what is  [#permalink]

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31 Oct 2018, 03:50
GMATinsight wrote:
Bunuel wrote:
If the diameter of circle A is eight times that of circle B, what is the ratio of the area of circle A to the area of circle B?

A. 4:1
B. 8:1
C. 16:1
D. 32:1
E. 64:1

$$\frac{D_A}{D_B} = \frac{8}{1}$$

Ratio of Areas $$= (\frac{D_A}{D_B})^2$$

i.e. $$\frac{Area of A}{Area of B} = (\frac{8}{1})^2 =\frac{64}{1}$$

I dont know how I messed this up but radius is half of diameter. So in the area ratio why is it not taken as half?
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If the diameter of circle A is eight times that of circle B, what is  [#permalink]

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31 Oct 2018, 07:55
MrCleantek wrote:
GMATinsight wrote:
Bunuel wrote:
If the diameter of circle A is eight times that of circle B, what is the ratio of the area of circle A to the area of circle B?

A. 4:1
B. 8:1
C. 16:1
D. 32:1
E. 64:1

$$\frac{D_A}{D_B} = \frac{8}{1}$$

Ratio of Areas $$= (\frac{D_A}{D_B})^2$$

i.e. $$\frac{Area of A}{Area of B} = (\frac{8}{1})^2 =\frac{64}{1}$$

I dont know how I messed this up but radius is half of diameter. So in the area ratio why is it not taken as half?

MrCleantek

Because ratio of Radius = Ratio of Diameters = Ratio of circumference
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Re: If the diameter of circle A is eight times that of circle B, what is  [#permalink]

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02 Nov 2018, 16:02
Bunuel wrote:
If the diameter of circle A is eight times that of circle B, what is the ratio of the area of circle A to the area of circle B?

A. 4:1
B. 8:1
C. 16:1
D. 32:1
E. 64:1

We can let the diameter of circle A = 16 and the diameter of circle B = 2, so the radii of circles A and B are 8 and 1, respectively. Thus, the area of circle A is 64π and the area of circle B is π, yielding a ratio of:

64π/π = 64/1

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Re: If the diameter of circle A is eight times that of circle B, what is &nbs [#permalink] 02 Nov 2018, 16:02
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