№ 438
79/80 - (3/16 + 39/40) = (79/80 - 39/80) - 3/16 = 40/80 - 3/16 = 1/2 - 3/16 = 5/16
2/45 + (41/45 - 7/9) = ( 2/45 + 41/45) - 7/9 = 43/45 - 7/9 = 43/45 -35/45 = 8/45
7/15 - ( 2/15 + 1/5) = ( 7/15 -2/15) - 1/5 = 5/15 - 1/5 = 5/15 - 3/15 = 2/15
3/16 + (15/16 -5/8) = ( 3/16 + 15/16) - 5/8 = 18/16 - 5/8 = 9/8 - 5/8 = 4/8 = 1/2
№439
31/60 + (7/20 + 11/60) = (31/60 + 11/60) + 7/20 = 42/60 + 7/20 = 14/20 + 7/20 =
=21/20 = 1 1/20
53/54 - ( 1/6 + 7/9) = ( 53/54 - 7/9) - 1/6 = 11/54 -1/6 =11/54 - 9/54 = 2/54 = 1/27
13/35 + (23/35 - 2/7) = (13/35 + 23/35) - 2/7 = 36/35 - 2/7 = 36/35 - 10/35 = =26/35
7/16 - (3/4 - 5/16) = ( 7/16 + 5/16) - 3/4 = 12/16 - 3/4 = 3/4 - 3/4 = 0