Ответ:
1 сотка = 100 квадратных метров
20 - 10 = 10 минут = 50 м 2
200 - 5 = 195 лампочек исправных
195 : 200 = 39\40
9 - (4 7/12 + 17/18) = 3 17/36
1) 4 7/12 + 17/18 = 4 21/36 + 34/36 = 4 55/36 = 5 19/36
2) 9 - 5 19/36 = 3 17/36
11 2/19 - (3 17/19 + 6 14/19) = 9/19
1) 3 17/19 + 6 14/19 = 9 31/19 = 10 12/19
2) 11 2/19 - 10 12/19 = 10 21/19 - 10 12/19 = 9/19