(25/28-5/14)-(5/7-1/4)-1/28=
1) 25\28 - 5\14 = 25\28 - 10\28 = 15\28 2) 5\7 - 1\4 = 20\28 - 7\28 = 13\28 3) 15\28 - 13\28 - 1\28 = 1\28 ОТВЕТ: 1\28