Bài tập 71 trang 20 SBT Toán 6 Tập 2

\(\begin{array}{l}
A = \frac{5}{{13}} + \frac{{ - 5}}{7} + \frac{{ - 20}}{{41}} + \frac{8}{{13}} + \frac{{ - 21}}{{41}}\\
 = \left( {\frac{5}{{13}} + \frac{8}{{13}}} \right) + \left( {\frac{{ - 20}}{{41}} + \frac{{ - 21}}{{41}}} \right) + \frac{{ - 5}}{7}\\
 = 1 + \left( { - 1} \right) + \frac{{ - 5}}{7} = \frac{{ - 5}}{7}\\
B = \frac{{ - 5}}{9} + \frac{8}{{15}} + \frac{{ - 2}}{{11}} + \frac{4}{{ - 9}} + \frac{7}{{15}}\\
 = \frac{{ - 5}}{9} + \frac{8}{{15}} + \frac{{ - 2}}{{11}} + \frac{{ - 4}}{9} + \frac{7}{{15}}\\
 = \left( {\frac{{ - 5}}{9} + \frac{{ - 4}}{9}} \right) + \left( {\frac{8}{{15}} + \frac{7}{{15}}} \right) + \frac{{ - 2}}{{11}}\\
 =  - 1 + 1 + \frac{{ - 2}}{{11}} = \frac{{ - 2}}{{11}}
\end{array}\)

-- Mod Toán 6 HỌC247