А) (5/8 - 2/5) + 3/20 = (25/40 - 16/40) + 6/40 = 9/40 + 6/40 = 15/40 = 3/5.
б) 1/8 + (5/9 - 1/4) = 9/72 + (40/72 - 18/72) = 9/72 + 22/72 = 31/72.
в) 5/6 - (3/10 + 2/5) = 50/60 - (18/60 + 24/60) = 50/60 - 42/60 = 8/60 = 2/15.
г) (3/4 + 1/8) - 5/8 = (6/8 + 1/8) - 5/8 = 7/8 - 5/8 = 2/8 = 1/4.