Tính a) 5/7 + 7/8 b) 3/5 - 3/8 c) 2 1/4 * 3 2/5 d) 1/5 : 7/8

* Hướng dẫn giải

$\begin{array}{l}a)\frac{5}{7}+\frac{7}{8}=\frac{40}{56}+\frac{49}{56}=\frac{89}{56}\\ b)\frac{3}{5}-\frac{3}{8}=\frac{24}{40}-\frac{15}{40}=\frac{9}{40}\\ c)2\frac{1}{4}\times 3\frac{2}{5}=\frac{9}{4}\times \frac{17}{5}=\frac{153}{20}\\ d)\frac{1}{5}:\frac{7}{8}=\frac{1}{5}\times \frac{8}{7}=\frac{8}{35}\end{array}$