857. Вычислите: а) 8/18 − 8/27; б) 7/16 − 5/24; в) 2/11 − 1/12; г) 12/15 − 15/20; д) 9/28 − 11/35; е) 39/40 − 19/28.

1. \(\dfrac8{18}-\dfrac8{27}=\dfrac4{9}-\dfrac8{27}=\dfrac{12-8}{27}=\dfrac4{27}\).
2. \(\dfrac7{16}-\dfrac5{24}=\dfrac{21}{48}-\dfrac{10}{48}=\dfrac{11}{48}\).
3. \(\dfrac2{11}-\dfrac1{12}=\dfrac{24-11}{132}=\dfrac{13}{132}\).
4. \(\dfrac{12}{15}-\dfrac{15}{20}=\dfrac45-\dfrac34=\dfrac{16-15}{20}=\dfrac1{20}\).
5. \(\dfrac9{28}-\dfrac{11}{35}=\dfrac{45}{140}-\dfrac{44}{140}=\dfrac1{140}\).
6. \(\dfrac{39}{40}-\dfrac{19}{28}=\dfrac{273}{280}-\dfrac{190}{280}=\dfrac{83}{280}\).

Ответ: а) \(\dfrac4{27}\); б) \(\dfrac{11}{48}\); в) \(\dfrac{13}{132}\); г) \(\dfrac1{20}\); д) \(\dfrac1{140}\); е) \(\dfrac{83}{280}\).