-2 2/3 + 2 1/3 * ( - 15 3/7 - ( - 4,8) : 4/15)=3 1/3
нужны действия

Пошаговое объяснение:

1.

1) (3/4 - 4/5) * 7,8 = (15/20 - 16/20) * 7,8 = -1/20 * 7,8 = -0,05 * 7,8 = - 0,39

2) (2/3 + 4/7) * (-7/13) =

(14/21 + 12/21) * (-7/13) =

26/21 * (-7/13) = - 2/3 * 1/1 = -2/3

3) -0,39 - (-2/3) = -39/100 + 2/3 = -117/300 + 200/300 = 83/300

2.

1) (3/7 - 16/21) * (-2 2/7) =

(9/21 - 16/21) * (-16/7) =

-7/21 * (-16/7) = 16/21

2) (11/15 + 0,3) : (-12 2/5) = (11/15 + 3/10) : (-62/5) =

= (22/30 + 9/30) * (-5/62) = 31/30 * (-5/62) = - 1/6 * 1/2 = - 1/12

3) 16/21 + (- 1/12) = 64/84 - 7/84 = 57/84 = 19/28.

5/6 = 2х/3                  4/9 = 8х/45                   5х/12 = 2/3

2х * 6 = 3 * 5              8х * 9 = 45 * 4              5х * 3 = 12 * 2

12х = 15                     72х = 180                     15х = 24

х = 15 : 12                  х = 180 : 72                   х = 24 : 15

х = 1,25                      х = 2,5                           х = 1,6

6/7 = 10х/21               8/9 = 4х/27                  27/5х = 9/16   

10х * 7 = 21 * 6          4х * 9 = 27 * 8              5х * 9 = 27 * 16

70х = 126                   36х = 216                     45х = 432

х = 126 : 70                х = 216 : 36                  х = 432 : 45

х = 1,8                        х = 6                             х = 9,6