phân số thứ 3 là : 1/2- 1/6- 1/7 =4/21
Ta có : \(\frac{1}{7}\)= \(\frac{6}{42}\)
\(\frac{1}{6}\)= \(\frac{7}{42}\)
\(\frac{1}{2}\)= \(\frac{21}{42}\)
\(\Rightarrow\)\(\frac{21}{42}\) - [\(\frac{6}{42}\)+ \(\frac{7}{42}\)] = \(\frac{9}{42}\)
mà \(\frac{9}{42}\)= \(\frac{3}{14}\)
vậy SCT là \(\frac{3}{14}\)