Difference between revisions of "2005 AMC 10A Problems/Problem 2"

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==Problem==
 
==Problem==
For each pair of real numbers <math>a</math><math>\neq</math><math>b</math>, define the [[operation]] <math>\star</math> as
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For each pair of real numbers <math>a \neq b</math>, define the [[operation]] <math>\star</math> as
  
 
<math> (a \star b) = \frac{a+b}{a-b} </math>.
 
<math> (a \star b) = \frac{a+b}{a-b} </math>.
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<math> ((1 \star 2) \star 3) = \left(\left(\frac{1+2}{1-2}\right) \star 3\right) = (-3 \star 3) = \frac{-3+3}{-3-3} = 0 \Longrightarrow \mathrm{(C)}</math>
 
<math> ((1 \star 2) \star 3) = \left(\left(\frac{1+2}{1-2}\right) \star 3\right) = (-3 \star 3) = \frac{-3+3}{-3-3} = 0 \Longrightarrow \mathrm{(C)}</math>
  
==See Also==
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==Video Solution==
*[[2005 AMC 10A Problems]]
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CHECK OUT Video Solution: https://youtu.be/5g_m3_nck8E
  
*[[2005 AMC 10A Problems/Problem 1|Previous Problem]]
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==See also==
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{{AMC10 box|year=2005|ab=A|num-b=1|num-a=3}}
  
*[[2005 AMC 10A Problems/Problem 3|Next Problem]]
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[[Category:Introductory Number Theory Problems]]
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{{MAA Notice}}

Revision as of 21:00, 30 October 2020

Problem

For each pair of real numbers $a \neq b$, define the operation $\star$ as

$(a \star b) = \frac{a+b}{a-b}$.

What is the value of $((1 \star 2) \star 3)$?

$\mathrm{(A) \ } -\frac{2}{3}\qquad \mathrm{(B) \ } -\frac{1}{5}\qquad \mathrm{(C) \ } 0\qquad \mathrm{(D) \ } \frac{1}{2}\qquad \mathrm{(E) \ } \textrm{This\, value\, is\, not\, defined.}$

Solution

$((1 \star 2) \star 3) = \left(\left(\frac{1+2}{1-2}\right) \star 3\right) = (-3 \star 3) = \frac{-3+3}{-3-3} = 0 \Longrightarrow \mathrm{(C)}$

Video Solution

CHECK OUT Video Solution: https://youtu.be/5g_m3_nck8E

See also

2005 AMC 10A (ProblemsAnswer KeyResources)
Preceded by
Problem 1
Followed by
Problem 3
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All AMC 10 Problems and Solutions

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