/ - эта черточка будет означать дробь
номер 505
а) 3/4+3/20 = 15/20+3/20 = 18/20 = 9/10
б) 7/10+3/20 = 14/20+3/20 = 17/20
в) 2/7+4/35 = 10/35+4/35 = 14/35 = 2/5
г) 21/32+1/8 = 21/32+4/32 = 25/32
номер 507
а) 11/27+4/9 = 11/27+12/27 = 23/27
б) 8/11+5/44 = 32/44+5/44 = 37/44
в) 11/25+2/5 = 11/25+10/25 = 21/25
г) 1/6+13/36 = 6/36+13/36 = 19/36
номер 508
а) 9/28+3/7 = 9/28+12/28 = 21/28 = 3/4
б) 7/30+11/300 = 70/300+11/300 = 81/300
в) 1/40+3/5 = 1/40+24/40 = 25/40 = 5/8
г) 4/9+5/36 = 16/36+5/36 = 21/36 = 7/12