Bài 2: Tính:

a)  \(\frac{2}{7}\) + \(\frac{3}{5}\) ;         \(\frac{31}{35}\) -  \(\frac{2}{7}\)  ;          \(\frac{31}{35}\) - \(\frac{3}{5}\)  ;           \(\frac{3}{5}\)  + \(\frac{2}{7}\)  ;

b) \(\frac{3}{4}\) + \(\frac{1}{6}\) ;          \(\frac{11}{12}\) - \(\frac{3}{4}\) ;           \(\frac{11}{12}\) -  \(\frac{1}{6}\)              \(\frac{1}{6}\)  + \(\frac{3}{4}\) ;

Lời Giải:

Bài 2:

a) \(\frac{2}{7}\) + \(\frac{3}{5}\) = \(\frac{10}{35}\) + \(\frac{21}{35}\) = \(\frac{31}{35}\) ;

\(\frac{31}{35}\) -  \(\frac{2}{7}\) = \(\frac{31}{35}\)  - \(\frac{10}{35}\) = \(\frac{21}{35}\)  =  \(\frac{3}{5}\)

 \(\frac{31}{35}\) - \(\frac{3}{5}\) = \(\frac{31}{35}\) - \(\frac{21}{35}\) = \(\frac{10}{35}\) =  \(\frac{2}{7}\)

\(\frac{3}{5}\) +  \(\frac{2}{7}\)  = \(\frac{21}{35}\)  + \(\frac{10}{35}\)  = \(\frac{31}{35}\)

b) \(\frac{3}{4}\) + \(\frac{1}{6}\) = \(\frac{9}{12}\) + \(\frac{2}{12}\) = \(\frac{11}{12}\)  ;

\(\frac{11}{12}\) -  \(\frac{3}{4}\)  = \(\frac{11}{12}\)   - \(\frac{9}{12}\) = \(\frac{2}{12}\)  = \(\frac{1}{6}\)

\(\frac{11}{12}\)  - \(\frac{1}{6}\)  = \(\frac{11}{12}\)  - \(\frac{2}{12}\) = \(\frac{9}{12}\)  =  \(\frac{3}{4}\) 

\(\frac{1}{6}\) + \(\frac{3}{4}\)  =  \(\frac{2}{12}\) + \(\frac{9}{12}\)  = \(\frac{11}{12}\)