В) (2/5 - 2/7) : 2/7 * 2/5 = г) (5/6 - 3/10) : (3/10 + 2/15) =

В) (2/5 - 2/7) : 2/7 * 2/5 = (2/5 - 2/7) * 7/2 * 2/5 = (2/5 - 2/7) * 7/5 = 2/5 * 7/5 - 2/7 * 7/5 = 14/25 - 2/5 = 14/25 - 10/25 = (14 - 10)/25 = 4/25;

Ответ: 4/25.

г) (5/6 - 3/10) : (3/10 + 2/15) = (25/30 - 9/30) : (9/30 + 4/30) = (25 - 9)/30 : (9 + 4)/30 = 16/30 : 13/30 = 16/30 * 30/13 = 16/13;

Ответ: 16/13.