П.28 Найдите значение выражения:

a) 20/31 * (10/5 : 1 2/15 - 2 4/9 + 3 7/9) - 2 5/6 = 20/31 * (2 : (23/15) - 2 4/9 + 3 7/9) - 2 5/6 = 20/31 * (30/23 - 2 4/9 + 3 7/9) - 2 5/6 = 20/31 * (30/23 + 1 17/45) - 2 5/6 = 20/31 * (1380/1035 + 47/45) - 2 5/6 = 20/31 * (1380/1035 + 1081/1035) - 2 5/6 = 20/31 * (2461/1035) - 2 5/6 = 49220/31935 - 2 5/6 = 1.541 - 2.833 = -1.292
б) (2 1/15 - 1 5/9) : 2 1/3 + 1 2/5 * 2 6/7 - 3 1/7 = (31/15 - 14/9) : 7/3 + 7/5 * 20/7 - 22/7 = (93/45 - 70/45) : 7/3 + 4 - 22/7 = 23/45 * 3/7 + 4 - 22/7 = 23/105 + 4 - 22/7 = 23/105 + 420/105 - 330/105 = 113/105 = 1 8/105
в) 25,48
г) 15/16 : 15/16 = 1