5/3x = 9/40+0,4
5/3x = 5/8
x = 5/8:5/3
x = 3/8
\(\frac{5}{3}x-0,4=\frac{9}{40}\)
\(\Rightarrow\frac{5}{3}x=\frac{9}{40}+0,4\)
\(\Rightarrow\frac{5}{3}x=\frac{5}{8}\)
\(\Rightarrow x=\frac{5}{8}:\frac{5}{3}\)
\(\Rightarrow x=\frac{3}{8}\)
vậy x=\(\frac{3}{8}\)