a. $\dfrac{-1}{12}+\dfrac{-5}{6}+\dfrac43=\left(\dfrac{-1}{12}+\dfrac43\right)+\dfrac{-5}{6}$
$= \dfrac{5}{4}+\dfrac{-5}{6}=\dfrac{-5}{12}$
b. $\dfrac{-24}{11}+\dfrac{-19}{13}+\dfrac2{11}+\dfrac{20}{13}=\left(\dfrac{-24}{11}+\dfrac2{11}\right)+\left(\dfrac{-19}{13}+\dfrac{20}{13}\right)=-2+\dfrac1{13}=\dfrac{-25}{13}$
c. $\dfrac{-3}{16}+\dfrac{-3}8+\dfrac{-5}4=\dfrac{-3}{16}+\dfrac{-6}{16}+\dfrac{-20}{16}=\dfrac{-29}{16}$
d. $\dfrac{-25}{13}+\dfrac{-9}{17}+\dfrac{12}{13}+\dfrac{-25}{17}=\left(\dfrac{-25}{13}+\dfrac{12}{13}\right)+\left(\dfrac{-9}{17}+\dfrac{-25}{17}\right)=-1-2=-3$
