А) (5/8 - 2/5) + 3/20 = ( 25/40 - 16/40) + 6/40 = 9/40 + 6/40 = 15/40 = 3/8.
б) 1/8 + ( 5/9 - 1/4) = 1/8 + ( 20/36 - 9/36) = 1/8 + 11/36 = 9/72 + 22/72= 31/72.
в) 5/6 - ( 3/10 + 2/5 ) = 5/6 - ( 3/10 + 4/10) = 5/6 - 7/10 = 25/30 - 21/30 = 4/30 = 2/15.
г) (3/4 + 1/8) - 5/8 = (6/8 + 1/8) - 5/8= 7/8 - 5/8= 2/8= 1/4