[9/10-4/5]:2/5 1

Lời giải:

\(\begin{array}{l}(\frac{9}{{10}} - \frac{4}{5}):\frac{2}{5} + 1\\ = \left( {\frac{9}{{10}} - \frac{8}{{10}}} \right).\frac{5}{2} + 1\\ = \frac{1}{{10}}.\frac{5}{2} + 1 = \frac{1}{4} + 1 = \frac{5}{4}\end{array}\)