Câu 1. (2 điểm) Tính.
a) $\dfrac{1}{3}+\dfrac{3}{4}-\dfrac{5}{6}$ ;
b) $\dfrac{-2}{3}+\dfrac{6}{5}:\dfrac{2}{3}-\dfrac{2}{15}$ ;
c) $\dfrac{-3}{7}+\dfrac{5}{13}+\dfrac{-4}{7}$ ;
d) $\dfrac{12}{19}+\dfrac{-8}{13}-\dfrac{12}{19}+\dfrac{5}{-13}+2$ .