6/7 : 3/5 * 1 2/5 = 6/7 * 5/3 * 7/5 = (6/7 * 7/5) * 5/3 = 6/5 * 5/3 = 6/3 = 2.
А теперь по действиям:
1) 6/7 : 3/5 = 6/7 * 5/3 = (2*5)/(7*1) = 10/7
2) 10/7 * 1 2/5 = 10/7 * 7/5 = 10/5 = 2
Ответ: 2.
12 - 5 = 12 - (2 + 3) = (12 - 2) - 3 = 10 - 3 = 7
11 - 4 = 11 - (1 + 3) = (11 - 1) - 3 = 10 - 3 = 7
14 - 6 = 14 - (4 + 2) = (14 - 4) - 2 = 10 - 2 = 8
1)0,75:1000=750(м)-длинна
2)750*10,5=7875(м^2)-площадь
7,875(км^2)