1)0,8+3/7 2)3 3/7 -2,5 3)4,9 +1 1/9

1) 8/10 + 3/7 = 56/70 + 30/70 = 86/70 2) 3 3/7 - 2,5 = 11/7 - 25/10 = 110/70 - 135/70 = 25/70 3) 4,9 + 11/9 = 49/10 + 11/9 = 441/90 + 110/90 = 551/90