Difference between revisions of "2007 AMC 12B Problems/Problem 3"

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==Problem==
 
==Problem==
 
 
The point <math>O</math> is the center of the circle circumscribed about triangle <math>ABC</math>, with <math>\angle BOC = 120^{\circ}</math> and <math>\angle AOB = 140^{\circ}</math>, as shown. What is the degree measure of <math>\angle ABC</math>?
 
The point <math>O</math> is the center of the circle circumscribed about triangle <math>ABC</math>, with <math>\angle BOC = 120^{\circ}</math> and <math>\angle AOB = 140^{\circ}</math>, as shown. What is the degree measure of <math>\angle ABC</math>?
  
{{image}}
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[[Image:2007_12B_AMC-3.png]]
  
<math>\mathrm {(A)} 35</math>  <math>\mathrm {(B)} 40</math>  <math>\mathrm {(C)} 45</math>  <math>\mathrm {(D)} 50</math>  <math>\mathrm {(E)} 60</math>
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<math>\mathrm {(A)} 35 \qquad \mathrm {(B)} 40 \qquad \mathrm {(C)} 45 \qquad \mathrm {(D)} 50 \qquad  \mathrm {(E)} 60</math>
  
 
==Solution==
 
==Solution==
 
 
 
<math>\angle AOC=360-140-120=100=2\angle ABC</math>
 
<math>\angle AOC=360-140-120=100=2\angle ABC</math>
  
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==See Also==
 
==See Also==
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{{AMC12 box|year=2007|ab=B|num-b=2|num-a=4}}
  
{{AMC12 box|year=2007|ab=B|num-b=2|num-a=4}}
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[[Category:Introductory Algebra Problems]]

Revision as of 16:29, 17 October 2007

Problem

The point $O$ is the center of the circle circumscribed about triangle $ABC$, with $\angle BOC = 120^{\circ}$ and $\angle AOB = 140^{\circ}$, as shown. What is the degree measure of $\angle ABC$?

2007 12B AMC-3.png

$\mathrm {(A)} 35 \qquad \mathrm {(B)} 40 \qquad \mathrm {(C)} 45 \qquad \mathrm {(D)} 50 \qquad  \mathrm {(E)} 60$

Solution

$\angle AOC=360-140-120=100=2\angle ABC$

$\angle ABC=50 \Rightarrow \mathrm {D}$

See Also

2007 AMC 12B (ProblemsAnswer KeyResources)
Preceded by
Problem 2
Followed by
Problem 4
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 12 Problems and Solutions