Tìm giá trị của x biết: (a) x − 7 , 5 : 1 , 5 = 100 , 8 − 105 . (b) ( 5 , 5 − 2 x ) : 3/7 = 2 1/3 .

a) \(x - 7,5:1,5 = 100,8 - 105\).

\(x - 5 = - 4,2\)

\(x = - 4,2 + 5\)

\(x = 0,8\).

Vậy \(x = 0,8\).

b) \(\left( {5,5 - 2x} \right):\frac{3}{7} = 2\frac{1}{3}\).

\(5,5 - 2x = \frac{7}{3}.\frac{3}{7}\)

\(5,5 - 2x = 1\)

\(2x = 5,5 - 1\)

\(2x = 4,5\)

\(x = \frac{9}{4}\).

Vậy \(x = \frac{9}{4}\).

c) \(\frac{{11}}{{66}} + \frac{2}{{15}}.x = \frac{4}{5}\).

\(\frac{1}{6} + \frac{2}{{15}}.x = \frac{4}{5}\)

\(\frac{2}{{15}}.x = \frac{4}{5} - \frac{1}{6}\)

\(\frac{2}{{15}}.x = \frac{{19}}{{30}}\)

\(x = \frac{{19}}{{30}}:\frac{2}{{15}}\)

\(x = \frac{{19}}{4}\).

Vậy \(x = \frac{{19}}{4}\).