У нас контрольная работа ​

Пошаговое объяснение:

(1)

а) 4/13 * 39/40 = 3/10

б) 6 2/3 * 12 3/4 = 20/3 * 51/4 =  85

в) 9/25 : 1 2/5 = 9/25 : 7/5 = 9/25 * 5/7 = 9/35

г) 9 : 81/90 = 9 * 90/81 = 90/9 = 10

(2)

(1/2)x = 4 6/12

x = 4 6/12 : 1/2

x = 54/12 * 2

x = 54/6

x = 9

проверка:

(1/2)*9 = 4 6/12

9/2 = 4 1/2

4 1/2 = 4 1/2

(2/3)b - 6 = 12

(2/3)b = 12 + 6

(2/3)b = 18

b = 18 * 3/2

b = 27

проверка:

(2/3)*27 - 6 = 12

18 - 6 = 12

12 = 12

(3)

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

2) 3 1/5 * 1 3/4 = 16/5 * 7/4 = 28/5

3) 3 2/5 : 1/4 = 17/5 * 4 = 68/5

4) 28/5 + 68/5 = 96/5 = 19 1/2