Выполните действия: а) 13/9 + 1/12; б) 7/24 + 1/60; в) 1/42 + 2/63; г) 5/12 + 3/20; д) 7/12 − 8/15; е) 25/39 − 15/26; ж) 7/15 − 8/25; з) 7/45 − 7/60.

Приведём дроби к общему знаменателю и выполним действия.

1. \(\dfrac{13}{9}+\dfrac{1}{12}=\dfrac{52}{36}+\dfrac{3}{36}=\dfrac{55}{36}=1\dfrac{19}{36}\).

2. \(\dfrac{7}{24}+\dfrac{1}{60}=\dfrac{35}{120}+\dfrac{2}{120}=\dfrac{37}{120}\).

3. \(\dfrac{1}{42}+\dfrac{2}{63}=\dfrac{3}{126}+\dfrac{4}{126}=\dfrac{7}{126}=\dfrac{1}{18}\).

4. \(\dfrac{5}{12}+\dfrac{3}{20}=\dfrac{25}{60}+\dfrac{9}{60}=\dfrac{34}{60}=\dfrac{17}{30}\).

5. \(\dfrac{7}{12}-\dfrac{8}{15}=\dfrac{35}{60}-\dfrac{32}{60}=\dfrac{3}{60}=\dfrac{1}{20}\).

6. \(\dfrac{25}{39}-\dfrac{15}{26}=\dfrac{50}{78}-\dfrac{45}{78}=\dfrac{5}{78}\).

7. \(\dfrac{7}{15}-\dfrac{8}{25}=\dfrac{35}{75}-\dfrac{24}{75}=\dfrac{11}{75}\).

8. \(\dfrac{7}{45}-\dfrac{7}{60}=\dfrac{28}{180}-\dfrac{21}{180}=\dfrac{7}{180}\).

Ответ: а) \(1\dfrac{19}{36}\); б) \(\dfrac{37}{120}\); в) \(\dfrac{1}{18}\); г) \(\dfrac{17}{30}\); д) \(\dfrac{1}{20}\); е) \(\dfrac{5}{78}\); ж) \(\dfrac{11}{75}\); з) \(\dfrac{7}{180}\).