1) 3 целых 3/4 + 2 целых 4/7 = 15/4 + 18/7 = 105/28 + 72/28 = 177/28 = 6 целых 9/28.
2) 2 целых 4/9 - 1 целая 5/6 = 22/9 - 11/6 = 44/18 - 33/18 = 11/18.
3) 7 целых 11/15 - (3 целых 9/20 +1 целая 1/30) = 116/15 - (69/20 + 31/30) = 116/15 - (207/60 + 62/60) = 116/15 - 269/60 = 464/60 - 269/60 = 195/60 = 39/12 = 13/4 = 3 целых 1/4