\(\times+\left(\times+1\right)+\cdot\cdot\cdot+\left(\times+10\right)=660\)
\(\Rightarrow11\times+\left(1+2+\cdot\cdot\cdot+10\right)=660\)
\(\Rightarrow11\times+55=660\)
\(\Rightarrow11\times=660-55\)
\(\Rightarrow11\times=605\)
\(\Rightarrow\times=55\)
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