Ответ:

а) \(\frac{3{,}1}{1{,}7}+\frac{6{,}7}{5{,}1}=\frac{31}{17}+\frac{67}{51}=\frac{93+67}{51}=\frac{160}{51}\).

б) \(\frac{2{,}5}{4{,}4}+\frac{4{,}6}{13{,}2}=\frac{25}{44}+\frac{23}{66}=\frac{75+46}{132}=\frac{11}{12}\).

в) \(\frac{6{,}8}{7{,}2}-\frac{2{,}7}{3{,}6}=\frac{17}{18}-\frac{3}{4}=\frac{34-27}{36}=\frac{7}{36}\).

г) \(\frac{2{,}4}{7{,}7}-\frac{2{,}8}{12{,}1}=\frac{24}{77}-\frac{28}{121}=\frac{264-196}{847}=\frac{68}{847}\).

Ответ: а) \(\frac{160}{51}\); б) \(\frac{11}{12}\); в) \(\frac{7}{36}\); г) \(\frac{68}{847}\).