[tex]-\dfrac{3}{10}+\dfrac{2}{3}=\dfrac{2}{3}+\left(-\dfrac{3}{10}\right)=\dfrac{2}{3}-\dfrac{3}{10}\\\\\text{We must find the common denominator.}\\\\Multiples\ of\ 3:0,\ 3,\ 6,\ 9,\ 12,\ 15,\ 18,\ 21,\ 24,\ 27,\ \boxed{30},\ 33,\ 36,...\\\\Multiples\ of\ 10:\ 0,\ 10,\ 20,\ \boxed{30},\ 40,\ 50,\ 60,...\\\\\dfrac{2}{3}=\dfrac{2\cdot10}{3\cdot10}=\dfrac{20}{30}\\\\\dfrac{3}{10}=\dfrac{3\cdot3}{10\cdot3}=\dfrac{9}{30}\\\\\dfrac{2}{3}-\dfrac{3}{10}=\dfrac{20}{30}-\dfrac{9}{30}=\dfrac{20-9}{30}=\dfrac{11}{30}[/tex]
