2 5/6*4/15+2 1/6*4/15=?

Выполняем сначала умножение, а после этого прибавление:

2 5/6 * 4/15 + 2 1/6 * 4/15 = 1 1/3.

1) 2 5/6 * 4/15 = (2 * 6 + 5) / 6 * 4/15 = (12 + 5) / 6 * 4/15 = 17/6 * 4/15 = (17 * 4) / (6 * 15) = (17 * 2 * 2) / (2 * 3 * 15) = (17 * 2) / (3 * 15) = 34/45;

2) 2 1/6 * 4/15 = (2 * 6 + 1) / 6 * 4/15 = (12 + 1) / 6 * 4/15 = 13/6 * 4/15 = (13 * 4) / (6 * 15) = (13 * 2 * 2) / (2 * 3 * 15) = (13 * 2) / (3 * 15) = 26/45;

3) 34/45 + 26/45 = (34 + 26) / 45 = 60/45 = 1 (60 - 1 * 45) / 45 = 1 (60 - 45) / 45 = 1 15/45 = 1 15 / (3 * 15) = 1 1/3.