

(2 intermediate revisions by 2 users not shown) 
Line 1: 
Line 1: 
−  ==Problem==
 +  #redirect [[2010 AMC 12B Problems/Problem 10]] 
−  The average of the numbers <math>1, 2, 3,\cdots, 98, 99,</math> and <math>x</math> is <math>100x</math>. What is <math>x</math>?
 
−   
−  <math>\textbf{(A)}\ \dfrac{49}{101} \qquad \textbf{(B)}\ \dfrac{50}{101} \qquad \textbf{(C)}\ \dfrac{1}{2} \qquad \textbf{(D)}\ \dfrac{51}{101} \qquad \textbf{(E)}\ \dfrac{50}{99}</math>
 
−   
−  ==Solution==
 
−  We must find the average of the numbers from <math> 1 </math> to <math> 99 </math> and <math> x </math> in terms of <math> x </math>. The sum of all these terms is <math> \frac{99(100)}{2}+x=99(50)+x </math>. We must divide this by the total number of terms, which is <math> 100 </math>. We get: <math> \frac{99(50)+x}{100} </math>. This is equal to <math> 100x </math>, as stated in the problem. We have: <math> \frac{99(50)+x}{100}=100x </math>. We can now cross multiply. This gives:
 
−   
−  \[\begin{align*}
 
−  100(100x)=99(50)+x&\\
 
−  10000x=99(50)+x&\\
 
−  9999x=99(50)&\\
 
−  101x=50&\\
 
−  x=\boxed{\textbf{(B)}\ \frac{50}{101}}&\\
 
−  \end{align*}\]
 
−   
−  ==See Also==
 
−  {{AMC10 boxyear=2010ab=Bnumb=13numa=15}}
 
−  {{MAA Notice}}
 