Thực hiện phép tính: a) 7/11 +5/3; b) 2/15 - 1/20

* Hướng dẫn giải

a)

$$\begin{gathered} \frac{7}{11}+\frac{5}{3}=\frac{7.3}{11.3}+\frac{5.11}{3.11}=\frac{21}{33}+\frac{55}{33} \\ =\frac{21+55}{33}=\frac{76}{33} \end{gathered}$$

b)

$$\begin{gathered} \frac{2}{15}-\frac{1}{20}=\frac{2.4}{15.4}-\frac{1.3}{20.3}=\frac{8}{60}-\frac{3}{60} \\ =\frac{5}{60}=\frac{1}{12} \end{gathered}$$