Difference between revisions of "2006 AMC 12A Problems/Problem 12"

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== Problem ==
 
== Problem ==
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A number of linked rings, each 1 cm thick, are hanging on a peg. The top ring has an outisde diameter of 20 cm. The outside diameter of each of the outer rings is 1 cm less than that of the ring above it. The bottom ring has an outside diameter of 3 cm. What is the distance, in cm, from the top of the top ring to the bottom of the bottom ring?  
 
 
A number of linked rings, each 1 cm thick, are hanging on a peg. The top ring has an outside [[diameter]] of 20 cm. The outside diameter of each of the outer rings is 1 cm less than that of the ring above it. The bottom ring has an outside diameter of 3 cm. What is the distance, in cm, from the top of the top ring to the bottom of the bottom ring?
 
 
 
<math> \mathrm{(A) \ } 171\qquad \mathrm{(B) \ } 173\qquad \mathrm{(C) \ } 182\qquad \mathrm{(D) \ } 188</math><math>\mathrm{(E) \ }  210</math>
 
  
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<math>\mathrm{(A) \ } 171\qquad\mathrm{(B) \ } 173\qquad\mathrm{(C) \ } 182\qquad\mathrm{(D) \ } 188\qquad\mathrm{(E) \ } 210\qquad</math>
 
== Solution ==
 
== Solution ==
The sum of the consecutively increasing [[integer]]s from 3 to 20 is <math> \frac{1}{2}(18)(3+20) = 207 </math>. However, the 17 [[intersection]]s between the rings must also be subtracted, so we get <math> 207 - 2(17) = 173 \Rightarrow B </math>.
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== See Also ==
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*[[2006 AMC 10A Problems]]
  
== See also ==
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*[[2006 AMC 10A Problems/Problem 13|Previous Problem]]
* [[2006 AMC 12A Problems]]
 
  
{{AMC12 box|year=2006|ab=A|num-b=11|num-a=13}}
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*[[2006 AMC 10A Problems/Problem 15|Next Problem]]
  
 
[[Category:Introductory Algebra Problems]]
 
[[Category:Introductory Algebra Problems]]
 
[[Category:Introductory Geometry Problems]]
 
[[Category:Introductory Geometry Problems]]
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Solution
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Add the inner diameters, which go from 18 down to 1. Then add 2 more for the thickness of the top and bottom rings.
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(18)(19)/2 + 2 = 173
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(B)

Revision as of 21:28, 14 February 2007

Problem

A number of linked rings, each 1 cm thick, are hanging on a peg. The top ring has an outisde diameter of 20 cm. The outside diameter of each of the outer rings is 1 cm less than that of the ring above it. The bottom ring has an outside diameter of 3 cm. What is the distance, in cm, from the top of the top ring to the bottom of the bottom ring?

$\mathrm{(A) \ } 171\qquad\mathrm{(B) \ } 173\qquad\mathrm{(C) \ } 182\qquad\mathrm{(D) \ } 188\qquad\mathrm{(E) \ } 210\qquad$

Solution

See Also

Solution

Add the inner diameters, which go from 18 down to 1. Then add 2 more for the thickness of the top and bottom rings. (18)(19)/2 + 2 = 173

(B)