31. -\frac{9}{11}+\frac{1}{3} = 32. -2\frac{6}{11}+1\frac{1}{2} = 33. -\frac{2}{3}+1\frac{7}{10} = 34. 3\frac{2}{9}+(-5\frac{1}{2}) = 35. -1\frac{1}{3}+4\frac{2}{21} = 36. -\frac{1}{4}+1,3 = 37. -1,2+\frac{3}{25}

Ответ: 31) -\frac{16}{33}; 32) -1\frac{1}{22}; 33) 1\frac{1}{30}; 34) -2\frac{13}{18}; 35) 2\frac{20}{21}; 36) 1,05; 37) -1,08

Решение:

31. −$$\frac{9}{11}$$ + $$\frac{1}{3}$$ =$$\frac{-9\cdot3 + 1\cdot 11}{33}$$ =$$\frac{-27+11}{33}$$ = −$$\frac{16}{33}

32. −2$$\frac{6}{11}$$ + 1$$\frac{1}{2}$$ = −$$\frac{28}{11}$$ + $$\frac{3}{2}$$ =$$\frac{-28\cdot2 + 3\cdot 11}{22}$$ =$$\frac{-56+33}{22}$$ = −$$\frac{23}{22}$$ = -1$$\frac{1}{22}

33. −$$\frac{2}{3}$$ + 1$$\frac{7}{10}$$ = −$$\frac{2}{3}$$ + $$\frac{17}{10}$$ =$$\frac{-2\cdot10 + 17\cdot 3}{30}$$ =$$\frac{-20+51}{30}$$ = $$\frac{31}{30}$$ = 1$$\frac{1}{30}

34. 3$$\frac{2}{9}$$ + (−5$$\frac{1}{2}$$) = $$\frac{29}{9}$$ + (−$$\frac{11}{2}$$) =$$\frac{29\cdot2 - 11\cdot 9}{18}$$ =$$\frac{58-99}{18}$$ = −$$\frac{41}{18}$$ = -2$$\frac{13}{18}

35. −1$$\frac{1}{3}$$ + 4$$\frac{2}{21}$$ = −$$\frac{4}{3}$$ + $$\frac{86}{21}$$ =$$\frac{-4\cdot7 + 86}{21}$$ =$$\frac{-28+86}{21}$$ = $$\frac{58}{21}$$ = 2$$\frac{16}{21}

36. −$$\frac{1}{4}$$ + 1,3 = -0,25 + 1,3 = 1,05

37. −1,2 + $$\frac{3}{25}$$ = -1,2 + 0,12 = -1,08

Ответ: 31) -\frac{16}{33}; 32) -1\frac{1}{22}; 33) 1\frac{1}{30}; 34) -2\frac{13}{18}; 35) 2\frac{20}{21}; 36) 1,05; 37) -1,08