Ответ:

  1. \(8+\frac{4}{21}=8\frac{4}{21}\);
  2. \(\frac{14}{33}+5=5\frac{14}{33}\);
  3. \(6\frac{4}{9}+3\frac{5}{9}=9\frac{9}{9}=10\);
  4. \(7\frac{7}{16}-3\frac{3}{16}=4\frac{4}{16}=4\frac14\);
  5. \(\frac78+\frac35=\frac{35}{40}+\frac{24}{40}=\frac{59}{40}=1\frac{19}{40}\);
  6. \(\frac45-\frac7{15}=\frac{12}{15}-\frac7{15}=\frac5{15}=\frac13\);
  7. \(\frac12+\frac34+\frac56=\frac6{12}+\frac9{12}+\frac{10}{12}=\frac{25}{12}=2\frac1{12}\);
  8. \(\frac35+\frac13+\frac7{12}=\frac{36}{60}+\frac{20}{60}+\frac{35}{60}=\frac{91}{60}=1\frac{31}{60}\);
  9. \(\frac{23}{24}-\frac5{12}-\frac16=\frac{23}{24}-\frac{10}{24}-\frac4{24}=\frac9{24}=\frac38\);
  10. \(\frac56-\frac18+\frac5{12}=\frac{20}{24}-\frac3{24}+\frac{10}{24}=\frac{27}{24}=1\frac18\);
  11. \(3\frac57+4\frac9{14}-2\frac5{21}=\frac{74}{21}+\frac{135}{21}-\frac{47}{21}=\frac{162}{21}=7\frac57\);
  12. \(2\frac13+\frac15-\frac18=\frac{56}{24}+\frac6{24}-\frac3{24}=\frac{59}{24}=2\frac{11}{24}\).

Ответ: \(8\frac4{21};\ 5\frac{14}{33};\ 10;\ 4\frac14;\ 1\frac{19}{40};\ \frac13;\ 2\frac1{12};\ 1\frac{31}{60};\ \frac38;\ 1\frac18;\ 7\frac57;\ 2\frac{11}{24}\).