Tìm x, biết: x + 1/ 2 + x + 1/ 3 + x + 1/ 4 = 1/8 .

Đáp án đúng là: D

\(\frac{{x + 1}}{2} + \frac{{x + 1}}{3} + \frac{{x + 1}}{4} = \frac{1}{8}\)

\((x + 1)\left( {\frac{1}{2} + \frac{1}{3} + \frac{1}{4}} \right) = \frac{1}{8}\)

\(x + 1 = \frac{1}{8}:\left( {\frac{1}{2} + \frac{1}{3} + \frac{1}{4}} \right)\)

\(x + 1 = \frac{1}{8}:\left( {\frac{6}{{12}} + \frac{4}{{12}} + \frac{3}{{12}}} \right)\)

\(x + 1 = \frac{1}{8}:\frac{{13}}{{12}}\)

\(x + 1 = \frac{3}{{26}}\)

\(x = \frac{3}{{26}} - 1\)

\(x = \frac{{ - 23}}{{26}}\).

Vậy \(x = \frac{{ - 23}}{{26}}\).