Ответ:

  1. (5/6 + 7/20) : 2 = (50/60 + 21/60) : 2 = 71/120 : 2 = 71/240.

  2. (1 3/7 + 2 5/21) : 2 = (1 9/21 + 2 5/21) : 2 = 3 2/3 : 2 = 11/6 : 2 = 11/12.

  3. (2 3/5 + 3 3/10 + 2 1/2) : 3 = (26/10 + 33/10 + 25/10) : 3 = 84/10 : 3 = 14/5.

  4. (7 5/24 + 6 7/24 + 8 1/6) : 3 = (173/24 + 151/24 + 196/24) : 3 = 520/24 : 3 = 65/9 = 7 2/9.