b) 25% -4 1/4 + 0,5 . 2 4/5

* Hướng dẫn giải

$\begin{array}{l}b) 25\%-4\frac{1}{4}+0,5.2\frac{4}{5}\\ =\frac{25}{100}-\frac{4.4+1}{4}+\frac{5}{10}.\frac{5.2+4}{5}\\ =\frac{1}{4}-\frac{17}{4}+\frac{5.2+4}{10}\\ =\frac{-\left(17+1\right)}{4}+\frac{14}{10}\\ =-4+\frac{7}{5}\\ =\frac{-4.5}{5}+\frac{7}{5}\\ =\frac{-20+7}{5}\\ =\frac{-13}{5}\end{array}$