Tính a) -3/8 + 2/5 b) 9/7 - 1/5 c) 7/11 -(-1/3) d) -11/33 -(1/-4)

* Hướng dẫn giải

a) $\frac{-3}{8}+\frac{2}{5}=\frac{-15+16}{40}=\frac{1}{40}$

b) $\frac{9}{7}-\frac{1}{5}=\frac{45-7}{35}=\frac{38}{35}$

c) $\frac{7}{11}-\left(-\frac{1}{3}\right)=\frac{7}{11}+\frac{1}{3}=\frac{21+11}{33}=1$

d) $\frac{-11}{33}-\left(\frac{1}{-4}\right)=\frac{-1}{3}+\frac{1}{4}=\frac{-4+3}{12}=\frac{-1}{12}$