Ответ:

  1. НОК(10,15)=30.

    \[3\frac{7}{10}-1\frac{4}{15}=3\frac{21}{30}-1\frac{8}{30}=2\frac{13}{30}.\]

  2. \[5\frac{1}{12}-2\frac{7}{15}=5\frac{5}{60}-2\frac{28}{60}=4\frac{65}{60}-2\frac{28}{60}=2\frac{37}{60}.\]

  3. НОК(35,20)=140.

    \[6\frac{9}{35}-5\frac{13}{20}=6\frac{36}{140}-5\frac{91}{140}=5\frac{176}{140}-5\frac{91}{140}=\frac{85}{140}=\frac{17}{28}.\]

  4. НОК(30,42)=210.

    \[4\frac{7}{30}-3\frac{5}{42}=4\frac{49}{210}-3\frac{25}{210}=3\frac{259}{210}-3\frac{25}{210}=\frac{234}{210}=1\frac{2}{15}.\]