## What are we learning ?

**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 .

## First look at the knowledge graph.

**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

##### Key Competency

### Ratio and Proportion

##### Difficulty Level

2/10

##### Suggested Book

**Start with hints**

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