2013 AMC 10B Problem 5

The expression is $2a-ab=a(2-b)$. To make it as small as possible, choose $b$ as large as possible so that $2-b$ is most negative, and choose $a$ as large as possible. Since $a,b<6$, take $a=b=5$. The minimum value is $5(2-5)=-15$. Thus, the correct answer is B .