Ta có: 1 / a + 1 / 4 = 3 / 8
=> 1 / a + 2 / 8 = 3 / 8
=> 1 / a = 3 / 8 - 2 / 8
=> 1 / a = 1 / 8
vậy 1/a = 1/8
\(\frac{1}{a}+\frac{1}{4}=\frac{3}{8}\)
\(\Leftrightarrow\)\(\frac{1}{a}=\frac{3}{8}-\frac{1}{4}=\frac{1}{8}\)
\(\Rightarrow a=8\)
Vậy \(a=8\)