Решите пример:(2целых 5/9 - 1целая 20/21) : 1целую 8/49 + 1целая

(2 5/9 - 1 20/21) : 1 8/49 + 1 8/9 : 6 = 5/6.

1) 2 5/9 - 1 20/21 = 2 - 1 + 5/9 - 20/21 = 1 + (5 * 7)/(9 * 7) - (20 * 3)/(21 * 3) = 1 + 35/63 - 60/63 = 1 - 25/63 = 63/63 - 25/63 = (63 - 25)/63 = 38/63;

2) 38/63 : 1 8/49 = 38/63 : (1 * 49 + 8)/49 = 38/63 : 57/49 = 38/63 * 49/57 = (19 * 2 * 7 * 7)/(7 * 9 * 19 * 3) = (2 * 7)/(9 * 3) = 14/27;

3) 1 8/9 : 6 = (1 * 9 + 8)/9 : 6 = 17/9 : 6 = 17/9 * 1/6 = 17/54;

4) 14/27 + 17/54 = (14 * 2)/(27 * 2) + 17/54 = 28/54 + 17/54 = (28 + 17)/54 = 45/54 = (5 * 9)/(6 * 9) = 5/6.