Tìm x biết

a) x : 2,2 = (28,7 – 13,5).2;

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

c) \(\frac{2}{3}x:\frac{1}{5} = 1\frac{1}{3}:25\% \);

d) \(0,5 - \left( {50\% - \frac{3}{5}x} \right) = 2\frac{1}{2}\)

Hướng dẫn giải:

a) x : 2,2 = (28,7 – 13,5).2

x : 2,2 = 15,2 . 2

x : 2,2 = 30,4

x = 30,4 . 2,2

x = 66,88

Vậy x = 66,88

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

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

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

\[x.\left( {\frac{1}{2} + \frac{2}{3}} \right) = \frac{1}{3} + \frac{2}{3}\]

\(x.\left( {\frac{3}{6} + \frac{4}{6}} \right) = 1\)

\(x.\frac{7}{6} = 1\)

\(x = 1:\frac{7}{6}\)

\(x = 1.\frac{6}{7}\)

\(x = \frac{6}{7}\)

Vậy \(x = \frac{6}{7}\)

c) \(\frac{2}{3}x:\frac{1}{5} = 1\frac{1}{3}:25\% \)

\(\frac{2}{3}x:\frac{1}{5} = \frac{4}{3}:\frac{1}{4}\)

\(\frac{2}{3}x.5 = \frac{4}{3}.4\)

\(\frac{{10}}{3}x = \frac{{16}}{3}\)

\(x = \frac{{16}}{3}:\frac{{10}}{3}\)

\(x = \frac{{16}}{3}.\frac{3}{{10}}\)

\(x = \frac{8}{5}\)

Vậy \(x = \frac{8}{5}\)

d) \(0,5 - \left( {50\% - \frac{3}{5}x} \right) = 2\frac{1}{2}\)

\(\frac{1}{2} - \left( {\frac{1}{2} - \frac{3}{5}x} \right) = \frac{5}{2}\)

\(\frac{1}{2} - \frac{1}{2} + \frac{3}{5}x = \frac{5}{2}\)

\(\left( {\frac{1}{2} - \frac{1}{2}} \right) + \frac{3}{5}x = \frac{5}{2}\)

\(\frac{3}{5}x = \frac{5}{2}\)

\(x = \frac{5}{2}:\frac{3}{2}\)

\(x = \frac{5}{2}.\frac{2}{3}\)

\(x = \frac{5}{3}\)

Vậy \(x = \frac{5}{3}\)