289. Вычислите значение выражения наиболее удобным способом: 1) 3/7 + 14/19 + 4/7 + 5/19; 2) 7/16 + 11/42 + 9/16 + 17/42; 3) 5/18 + 4/81 + 7/18 + 5/81; 4) 9/40 + 13/50 + 12/50 + 11/40; 5) 3 5/11 + 1 3/16 + 2 5/16 + 4 6/11; 6) 1 17/24 + 3 1/36 + 5 4/24 + 2 8/36.

1. \(\frac37+\frac47+\frac{14}{19}+\frac5{19}=1+1=2\).
2. \(\frac7{16}+\frac9{16}+\frac{11}{42}+\frac{17}{42}=1+\frac{28}{42}=1+\frac23=1\frac23\).
3. \(\frac5{18}+\frac7{18}+\frac4{81}+\frac5{81}=\frac{12}{18}+\frac9{81}=\frac23+\frac19=\frac79\).
4. \(\frac9{40}+\frac{11}{40}+\frac{13}{50}+\frac{12}{50}=\frac{20}{40}+\frac{25}{50}=\frac12+\frac12=1\).
5. \(3\frac5{11}+4\frac6{11}+1\frac3{16}+2\frac5{16}=7+\frac{11}{11}+3+\frac8{16}=8+3\frac12=11\frac12\).
6. \(1\frac{17}{24}+5\frac4{24}+3\frac1{36}+2\frac8{36}=6+\frac{21}{24}+5+\frac9{36}=6\frac78+5\frac14=11+\frac98=12\frac18\).

Ответ: 1) 2; 2) \(1\frac23\); 3) \(\frac79\); 4) 1; 5) \(11\frac12\); 6) \(12\frac18\).