tìm x biết x-2/5=7/10

a) \(x - \frac{2}{5} = \frac{7}{{10}}\)

\(x = \frac{7}{{10}} + \frac{2}{5}\)

\(x = \frac{7}{{10}} + \frac{4}{{10}}\)

\(x = \frac{{11}}{{10}}\).

Vậy \(x = \frac{{11}}{{10}}\).

b) \(\left( {2x - \frac{2}{3}} \right) \cdot \frac{5}{6} = \frac{5}{{18}}\)

\(\left( {2x - \frac{2}{3}} \right) = \frac{5}{{18}}:\frac{5}{6}\)

\(\left( {2x - \frac{2}{3}} \right) = \frac{5}{{18}} \cdot \frac{6}{5}\)

\(2x - \frac{2}{3} = \frac{1}{3}\)

\(2x = \frac{1}{3} + \frac{2}{3}\)

\(2x = 1\)

\(x = 1:2\)

\(x = \frac{1}{2}.\)

Vậy \(x = \frac{1}{2}.\)

c) \(1,5\left( {x - 3,4} \right) = 22,5\)

\(\left( {x - 3,4} \right) = 22,5:1,5\)

\(x - 3,4 = 15\)

\(x = 15 + 3,4\)

\(x = 18,4\).