Evaluate$$\left\textbar{} 3-9 \right\textbar+\left\textbar{} 7-2 \right\textbar$$. 
Overseas Competition->Knowledge Point->Combinatorics->Mathematical Thoughts->Absolute Value
$$\left\textbar{} 3-9 \right\textbar+\left\textbar{} 7-2 \right\textbar=\left\textbar{} -6 \right\textbar+\left\textbar{} 5 \right\textbar=6+5=11$$. 