1/4:3/4*х -1/2+2/5=1/2

$\frac{1}{4} : \frac{3}{4}*x - \frac{1}{2} + \frac{2}{5} = \frac{1}{2} \\ \\ \frac{1}{4} : \frac{3}{4}*x =\frac{1}{2} + \frac{1}{2} - \frac{2}{5} \\ \\ \frac{1}{4} * \frac{4}{3}* \frac{x}{1} = 1 - \frac{2}{5} \\ \\ \frac{x}{3} = \frac{3}{5} \\ \\ 5x=3*3 \\ \\ x=9 : 5 = \frac{9}{5} \\ \\ x=1 \frac{4}{5} \\ \\$

проверим:
$\frac{1}{4} : \frac{3}{4}*1 \frac{4}{5} - \frac{1}{2} + \frac{2}{5} = \frac{1}{2} \\ \\ \frac{1}{4} * \frac{4}{3}* \frac{9}{5} - \frac{1}{2} + \frac{2}{5} = \frac{1}{2} \\ \\ \frac{3}{5} - \frac{1}{2} + \frac{2}{5} = \frac{1}{2} \\ \\ \frac{3*2 -1* 5 + 2*2}{10} = \frac{1}{2} \\ \\ \frac{5}{10} = \frac{1}{2} \\ \\ \frac{1}{2} = \frac{1}{2}$