Bonjour,
a) 12/5 + 4/5 = (12 + 4)/5 = 16/5
b) 8/10 + 7/20 = (8/10) + (7/20) = (16/20) + (7/20) = 23/20
c) 44/9 - 5/3 = (44/9) - (15/9) = 29/9
d) 5/7 + 12/21 - 1/3 = (15/21) + (12/21) - (7/21) = 20/21
e) 33/25 - 6/5 + 14/50 = (33/25) - (30/25) + (14/50) = 17/25