Tính các tổng sau:

* Hướng dẫn giải

a) 3.              

b) 1.

$\begin{array}{l}c)\frac{1}{2}+\frac{-2}{3}+\frac{1}{6}+\frac{3}{7}=\frac{3}{6}+\frac{-4}{6}+\frac{1}{6}+\frac{3}{7}=\frac{3}{7};\\ \\ d)\frac{1}{2}+\frac{2}{8}+\frac{3}{4}+\frac{4}{5}+\frac{5}{6}=\frac{30}{60}+\frac{40}{60}+\frac{45}{60}+\frac{48}{60}+\frac{50}{60}=\frac{71}{5}\end{array}$