Difference between revisions of "2006 AMC 10B Problems/Problem 4"

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== See Also ==
 
== See Also ==
*[[2006 AMC 10B Problems]]
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{{AMC10 box|year=2006|ab=B|num-b=3|num-a=5}}
 
 
*[[2006 AMC 10B Problems/Problem 3|Previous Problem]]
 
 
 
*[[2006 AMC 10B Problems/Problem 5|Next Problem]]
 
  
 
[[Category:Introductory Geometry Problems]]
 
[[Category:Introductory Geometry Problems]]

Revision as of 21:52, 7 September 2011

Problem

Circles of diameter 1 inch and 3 inches have the same center. The smaller circle is painted red, and the portion outside the smaller circle and inside the larger circle is painted blue. What is the ratio of the blue-painted area to the red-painted area?

2006amc10b04.gif

$\mathrm{(A) \ } 2\qquad \mathrm{(B) \ } 3\qquad \mathrm{(C) \ } 6\qquad \mathrm{(D) \ } 8\qquad \mathrm{(E) \ } 9$

Solution

The area painted red is equal to the area of the smaller circle and the area painted blue is equal to the area of the larger circle minus the area of the smaller circle.

So:

$A_{red}=\pi(\frac{1}{2})^2=\frac{\pi}{4}$

$A_{blue}=\pi(\frac{3}{2})^2-\pi(\frac{1}{2})^2=2\pi$

So the desired ratio is:

$\frac{2\pi}{\frac{\pi}{4}}=8\Rightarrow D$

See Also

2006 AMC 10B (ProblemsAnswer KeyResources)
Preceded by
Problem 3
Followed by
Problem 5
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
All AMC 10 Problems and Solutions