Пошаговое объяснение:

№1

а)

1) 2 - 2 7/12 = -7/12

2) 3/8 - 1/6 = 9/24 - 4/24 = 5/24

3) -7/12 : 5/24 = -7/12 * 24/5 = -7/1 * 2/5 = -14/5

4) -14/5 * (-3 1/4) = -14/5 * (-13/4) = -7/5 * (-13/2) = 91/10 = 9 1/10

б)

1) -2 4/9 - 1 1/6 = -2 8/18 - 1 3/18 = -3 11/18

2) -3 11/18 * 1 4/5 = -65/18 * 9/5 = -13/2 * 1/1 = -13/2 = -6 1/2

3) 3 1/9 : (-2 1/3) = 28/9 : (-7/3) = 28/9 * (-3/7) = 4/3 * (-1/1) = -4/3 = -1 1/3

4) -6 1/2 - (-1 1/3) = -6 1/2 + 1 1/3 = -6 3/6 + 1 2/6 = -5 1/6

в)

1) 7/10 - 2/5 = 7/10 - 4/10 = 3/10

2) 1/4 + 5/6 = 3/12 + 10/12 = 13/12

3) 3/10 * 13/12 = 1/10 * 13/4 = 13/40

4) 13/40 : (-6 1/2) = 13/40 : (-13/2) = 13/40 * (-2/13) = 1/20 * (-1/1) = -1/20

№2

Задуманное число — х

х * (-6) + 16,9 = -8,9

-6х + 16,9 = -8,9

-6х = -8,9 - 16,9

-6х = -25,8

х = -25,8 : (-6)

х = 4,3