251. Найди значения выражений: 1) 1 5/16 + 11/12; 2) 5/21 + 5/28; 3) 15/19 + 27/38; 4) 9/16 + 19/24; 5) 9/20 − 5/12; 6) 7/18 − 1/45; 7) 11/42 − 5/28; 8) 13/60 − 7/40.

1. Приведём дроби к общему знаменателю: \(1\frac{5}{16}+\frac{11}{12}=1+\frac{15}{48}+\frac{44}{48}=2\frac{11}{48}\).
2. \(\frac{5}{21}+\frac{5}{28}=\frac{20}{84}+\frac{15}{84}=\frac{35}{84}=\frac{5}{12}\).
3. \(\frac{15}{19}+\frac{27}{38}=\frac{30}{38}+\frac{27}{38}=\frac{57}{38}=1\frac{19}{38}=1\frac{1}{2}\).
4. \(\frac{9}{16}+\frac{19}{24}=\frac{27}{48}+\frac{38}{48}=\frac{65}{48}=1\frac{17}{48}\).
5. \(\frac{9}{20}-\frac{5}{12}=\frac{27}{60}-\frac{25}{60}=\frac{2}{60}=\frac{1}{30}\).
6. \(\frac{7}{18}-\frac{1}{45}=\frac{35}{90}-\frac{2}{90}=\frac{33}{90}=\frac{11}{30}\).
7. \(\frac{11}{42}-\frac{5}{28}=\frac{22}{84}-\frac{15}{84}=\frac{7}{84}=\frac{1}{12}\).
8. \(\frac{13}{60}-\frac{7}{40}=\frac{26}{120}-\frac{21}{120}=\frac{5}{120}=\frac{1}{24}\).

Ответ: 1) 2 11/48; 2) 5/12; 3) 1 1/2; 4) 1 17/48; 5) 1/30; 6) 11/30; 7) 1/12; 8) 1/24.