a) 3/4 + 1/5 = 15/20 + 4/20 = 19/20
б) 2/3 + 1/7 = 14/21 + 3/21 = 17/21
в) 2/13 + 0 = 2/13
г) 5/9 + 2/11 = 55/99 + 18/99 = 73/99
д) 5/12 + 3/4 = 5/12 + 9/12 = 14/12 = 7/6
е) 5/6 + 7/8 = 20/24 + 21/24 = 41/24
Ответ: a) 19/20, б) 17/21, в) 2/13, г) 73/99, д) 7/6, е) 41/24