Вычислите 20-18,6: (6 11/15-4 3/20)

1) 6 11/15 - 4 3/20 = 101/15 - 83/20 = (101 * 4 - 83 * 3) / 60 = 404/60 - 249/60 = 155/60 = 31/12 = 2 7/12

2) 18,6 : 2 7/12=18 6/10 : 2 7/12 = 93/5 : 31/12 = 93/5 * 12/31 = 1116/155 = 36/5 = 7 1/5=7,2

3) 20-7,2=12,8

ответ 12,8