ными знаменателями. Случай 1 + 2-91-70 3 71 21) + 31) 21-2 75 450 273 22) 23) 4-7416 16 636 32) 28 81 9 S 46 4 33) 6 6 18 49 7 2 3 10 24) 34) 7 14 819 71 714 25) 35) 5 3 27 10-2 8 L 5 26) 36) 15 3 10 100 22 7 40 27) 37) 9 3 100 3 4 4 112 10 28) 38) 7 21 4 100 3 11 10 4 29) 39) 5 20 70 210 38 13 7 30) 40) 900 450 5 15

21) \[\frac{3}{75} + \frac{71}{450} = \frac{3 \cdot 6}{75 \cdot 6} + \frac{71}{450} = \frac{18}{450} + \frac{71}{450} = \frac{18 + 71}{450} = \frac{89}{450}\]

22) \[\frac{4}{7} - \frac{16}{28} = \frac{4 \cdot 4}{7 \cdot 4} - \frac{16}{28} = \frac{16}{28} - \frac{16}{28} = 0\]

23) \[\frac{4}{6} - \frac{5}{18} = \frac{4 \cdot 3}{6 \cdot 3} - \frac{5}{18} = \frac{12}{18} - \frac{5}{18} = \frac{12 - 5}{18} = \frac{7}{18}\]

24) \[\frac{2}{7} - \frac{3}{14} = \frac{2 \cdot 2}{7 \cdot 2} - \frac{3}{14} = \frac{4}{14} - \frac{3}{14} = \frac{4 - 3}{14} = \frac{1}{14}\]

25) \[\frac{7}{15} - \frac{1}{5} = \frac{7}{15} - \frac{1 \cdot 3}{5 \cdot 3} = \frac{7}{15} - \frac{3}{15} = \frac{7 - 3}{15} = \frac{4}{15}\]

26) \[\frac{10}{15} - \frac{2}{3} = \frac{10}{15} - \frac{2 \cdot 5}{3 \cdot 5} = \frac{10}{15} - \frac{10}{15} = 0\]

27) \[\frac{22}{9} - \frac{7}{3} = \frac{22}{9} - \frac{7 \cdot 3}{3 \cdot 3} = \frac{22}{9} - \frac{21}{9} = \frac{22 - 21}{9} = \frac{1}{9}\]

28) \[\frac{4}{7} - \frac{4}{21} = \frac{4 \cdot 3}{7 \cdot 3} - \frac{4}{21} = \frac{12}{21} - \frac{4}{21} = \frac{12 - 4}{21} = \frac{8}{21}\]

29) \[\frac{3}{5} - \frac{11}{20} = \frac{3 \cdot 4}{5 \cdot 4} - \frac{11}{20} = \frac{12}{20} - \frac{11}{20} = \frac{12 - 11}{20} = \frac{1}{20}\]

30) \[\frac{3}{5} - \frac{8}{15} = \frac{3 \cdot 3}{5 \cdot 3} - \frac{8}{15} = \frac{9}{15} - \frac{8}{15} = \frac{9 - 8}{15} = \frac{1}{15}\]

31) \[\frac{21}{27} - \frac{2}{3} = \frac{21}{27} - \frac{2 \cdot 9}{3 \cdot 9} = \frac{21}{27} - \frac{18}{27} = \frac{21 - 18}{27} = \frac{3}{27} = \frac{1}{9}\]

32) \[\frac{63}{81} - \frac{6}{9} = \frac{63}{81} - \frac{6 \cdot 9}{9 \cdot 9} = \frac{63}{81} - \frac{54}{81} = \frac{63 - 54}{81} = \frac{9}{81} = \frac{1}{9}\]

33) \[\frac{48}{49} - \frac{4}{7} = \frac{48}{49} - \frac{4 \cdot 7}{7 \cdot 7} = \frac{48}{49} - \frac{28}{49} = \frac{48 - 28}{49} = \frac{20}{49}\]

34) \[\frac{10}{64} - \frac{1}{8} = \frac{10}{64} - \frac{1 \cdot 8}{8 \cdot 8} = \frac{10}{64} - \frac{8}{64} = \frac{10 - 8}{64} = \frac{2}{64} = \frac{1}{32}\]

35) \[\frac{7}{3} - \frac{14}{27} = \frac{7 \cdot 9}{3 \cdot 9} - \frac{14}{27} = \frac{63}{27} - \frac{14}{27} = \frac{63 - 14}{27} = \frac{49}{27}\]

36) \[\frac{8}{10} - \frac{1}{100} = \frac{8 \cdot 10}{10 \cdot 10} - \frac{1}{100} = \frac{80}{100} - \frac{1}{100} = \frac{80 - 1}{100} = \frac{79}{100}\]

37) \[\frac{40}{100} - \frac{1}{5} = \frac{40}{100} - \frac{1 \cdot 20}{5 \cdot 20} = \frac{40}{100} - \frac{20}{100} = \frac{40 - 20}{100} = \frac{20}{100} = \frac{1}{5}\]

38) \[\frac{112}{4} - \frac{10}{100} = \frac{112 \cdot 25}{4 \cdot 25} - \frac{10}{100} = \frac{2800}{100} - \frac{10}{100} = \frac{2800 - 10}{100} = \frac{2790}{100} = 27 \frac{9}{10}\]

39) \[\frac{4}{10} - \frac{100}{4} = \frac{4 \cdot 2}{10 \cdot 2} - \frac{100}{4} = \frac{8}{20} - \frac{100 \cdot 5}{4 \cdot 5} = \frac{8}{20} - \frac{500}{20} = \frac{8 - 500}{20} = \frac{-492}{20} = -24 \frac{12}{20} = -24 \frac{3}{5}\]

40) \[\frac{70}{900} - \frac{210}{450} = \frac{70}{900} - \frac{210 \cdot 2}{450 \cdot 2} = \frac{70}{900} - \frac{420}{900} = \frac{70 - 420}{900} = \frac{-350}{900} = -\frac{35}{90} = -\frac{7}{18}\]

41) \[\frac{13}{900} - \frac{7}{450} = \frac{13}{900} - \frac{7 \cdot 2}{450 \cdot 2} = \frac{13}{900} - \frac{14}{900} = \frac{13 - 14}{900} = -\frac{1}{900}\]