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## Competency in Focus:Ratio and proportion.

This problem from American Mathematics contest (AMC 8, 2010) is based on the concept of ratio and proportion and binary composition .

## Next understand the problem

If $a @ b = \frac{a\times b}{a+b}$ for $a,b$ positive integers, then what is $5 @10$? $\textbf{(A)}\ \frac{3}{10} \qquad\textbf{(B)}\ 1 \qquad\textbf{(C)}\ 2 \qquad\textbf{(D)}\ \frac{10}{3} \qquad\textbf{(E)}\ 50$
##### Source of the problem
American Mathematical Contest 2010, AMC 8  Problem 2

### Ratio and Proportion

2/10
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Substitute $a \textbf{ by } 5 \textbf{ and } b \text{ by } 10$
$5@10=\frac{5\times10}{5+10}=\frac{50}{15}=\frac{10}{3}$

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