а) 5/10 + 1/11 = 55/110 + 10/110 = 65/110 = 13/22

б) 3/7 + 1/4 = 12/28 + 7/28 = 19/28

в) 3/5 + 2/15 = 9/15 + 2/15 = 11/15

г) 3/25 + 2/15 = 9/75 + 10/75 = 19/75

д) 3/5 - 2/5 = 1/5

е) 11/12 - 3/4 = 11/12 - 9/12 = 2/12 = 1/6

ж) 5/8 - 5/9 = 45/72 - 40/72 = 5/72

з) 5/21 - 3/28 = 20/84 - 9/84 = 11/84