1)) 2 / 6 + 4 / 30 - 7 / 15 = (2•5) / (6•5) + 4 / 30 - (7•2) / (15•2) = 10 / 30 + 4 / 30 - 14 / 30 = 14 / 30 - 14 / 30 = 0.
2)) 2 / 5 + 5 / 6 - 4 / 30 = (2•6) / (5•6) + (5•5) / (6•5) - 4 / 30 = 12 / 30 + 25 / 30 - 4 / 30 = 37 / 30 - 4 / 30 = 33 / 30 = 1 3 / 30 = 1 (3 : 3) / (30 : 3) = 1 1 / 10 = 1, 1
3)) 4 / 21 + 3 / 7 - 1 / 3 = 4 / 21 + (3•3) / (7•3) - (1•7) / (3•7) = 4 / 21 + 9 / 21 - 7 / 21 = 13 / 21 - 7 / 21 = 6 / 21 = (6 : 3) / (21 : 3) = 2 / 7
4)) 16 / 5 + 5 / 2 - 11 / 6 = (16•6) / (5•6) + (5•15) / (2•15) - (11•5) / (6•5) = 96 / 30 + 75 / 30 - 55 / 30 = 171 / 30 - 55 / 30 = 116 / 30 = 3 26 / 30 = 3 (26 : 2) / (30 : 2) = 3 13 / 15.
5)) 2 / 4 + 3 / 5 - 3 / 10 = (2 : 2) / (4 : 2) + 3 / 5 - 3 / 10 = 1 / 2 + 3 / 5 - 3 / 10 = (1•5) / (2•5) + (3•2) / (5•2) - 3 / 10 = 4 / 10 + 6 / 10 - 3 / 10 = 7 / 10 = 0, 7
6)) 1 / 4 + 1 / 2 - 5 / 12 = (1•3) / (4•3) + (1•6) / (2•6) - 5 / 12 = 3 / 12 + 6 / 12 - 5 / 12 = 4 / 12 = (4 : 4) / (12 : 4) = 1 / 3
7)) 25 / 7 + 23 / 8 - 5 / 14 = 25 / 7 - 5 / 14 + 23 / 8 = (25•2) / (7•2) - 5 / 14 + 23 / 8 = 50 / 14 - 5 / 14 + 23 / 8 = 45 / 14 + 23 / 8 = 3 3 / 14 + 2 7 / 8 = 3 (3•4) / (14•4) + 2 (7•7) / (8•7) = 3 12 / 56 + 2 49 / 56 = 5 61 / 56 = 6 5 / 56.