4) 17/20 - 3/10 - 11/60 = 51/60 - 18/60 - 11/60 = 22/60 = 11/30
5) 3/20 + 7/10 - 3/40 = 6/40 + 28/40 - 3/40 = 31/40
6) 9/40 + 3/4 - 19/20 = 9/40 + 30/40 - 38/40 = 1/40
№ 438
3) 7/15 - (2/15 + 1/5) = 7/15 - (2/15 + 3/15) = 7/15 - 5/15 = 2/15
4) 3/16 + (15/16 - 5/8) = 3/16 + (15/16 - 10/16) = 3/16 + 5/16 = 8/16 = 1/2