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Пошаговое объяснение:

17/20 + 11/15 = 51/60 + 44/60 = 95/60 = 1цел.35/60 = 1цел.7/12

19/42 - 5/63 = 57/126 - 10/126 = 47/126

16/21 + 13/15 = 80/105 + 91/105 = 171/105 = 1цел.66/105 = 1цел.22/35

21/22 - 3/55 = 105/110 - 6/110 = 99/110 = 9/10

ответ:17/20 + 11/15 = 51/60 + 44/60 = 95/60 = 1 7/12

19/42 - 5/63 = 57/126 - 10/126 = 47/126

16/21 + 13/15 = 80/105 + 91/105 = 171/105 = 1цел.66/105 = 1 22/35

21/22 - 3/55 = 105/110 - 6/110 = 99/110 = 9/10

Пошаговое объяснение: