a)$\frac{1}{5}$ x :3=$\frac{2}{3}$ :0,25
$\frac{1}{5}$ x :3=$\frac{2}{3}$ :$\frac{1}{4}$
$\frac{1}{5}$ x :3=$\frac{2}{3}$ ·4
$\frac{1}{5}$ x :3=$\frac{8}{3}$
$\frac{1}{5}$ x=$\frac{8}{3}$ ·3
$\frac{1}{5}$ x=8
x=8 :$\frac{1}{5}$
x=8·5=40
b)(x-1)³=27
(x-1)³=3³
x-1=3
x=4
tớ ln đúng 100% nha!!