1)
1) 1/4 + 5/6 = 3/12 + 10/12 = 13/12
2) 2/3 + 1/5 = 10/15 + 3/15 = 13/15
3) 1/6 + 3/8 = 4/24 + 9/24 = 13/24
4) 5/12 + 7/18 = 15/36 + 14/36 = 29/36

2)
1) 4/15 + 3/25 = 20/75 + 9/75 = 29/75
2) 9/16 + 5/24 = 135/240 + 100/240 = 235/240
3) 19/32 + 17/48 = 288/512 + 340/512 = 628/512 = 157/128
4) 41/45 + 43/50 = 410/450 + 387/450 = 797/450

3)
1) 5/9 + 1/12 = 20/36 + 3/36 = 23/36
2) 3/7 + 4/21 = 9/21 + 4/21 = 13/21
3) 4/35 + 4/21 = 12/105 + 20/105 = 32/105
4) 3/5 + 1/9 = 27/45 + 5/45 = 32/45

Надеюсь, вычисления верны.