Thực hiện phép tính (tính hợp lí nếu có thể):

- Hướng dẫn giải

$a)\frac{1}{12}+\frac{2}{3}+\frac{-3}{4}=\frac{1}{12}+\frac{8}{12}+\frac{-9}{12}=0$

$\begin{array}{l}b)\frac{1}{2}-\frac{2}{5}+\frac{-7}{10}=\frac{5}{10}-\frac{4}{10}+\frac{-7}{10}=\frac{-6}{10}=\frac{-3}{5}\\ \\ c)\frac{1}{2}+\frac{-3}{7}+\frac{5}{2}+\frac{-4}{7}=\left(\frac{1}{2}+\frac{5}{2}\right)+\left(\frac{-3}{7}+\frac{-4}{7}\right)=2\\ \\ \text{d})\frac{9}{8}-\frac{4}{7}+\frac{-1}{8}+\frac{11}{7}=\left(\frac{9}{8}+\frac{-1}{8}\right)+\left(\frac{-4}{7}+\frac{11}{7}\right)=2\\ \\ e)\frac{6}{11}+\left(\frac{-2}{3}+\frac{5}{11}\right)=\left(\frac{6}{11}+\frac{5}{11}\right)+\frac{-2}{3}=\frac{1}{3}\\ \\ f)\frac{-1}{2}+\frac{11}{4}-\left(\frac{11}{4}-\frac{1}{2}\right)=\frac{-1}{2}+\frac{11}{4}-\frac{11}{4}+\frac{1}{2}=0\end{array}$