30 5/6 - (7 1/3 + 2 1/4) : 0,25

30 5/6 - (7 1/3 + 2 1/4) : 0,25 = - 7,5

1) 7 1/3 + 2 1/4 = 7 4/12 + 2 3/12 = 9 7/12

2) 9 7/12 : 0,25 = 115/12 : 1/4 = 115/12 * 4/1 = (115*1) / (3*1) = 115/3 =

= 38 1/3

3) 30 5/6 - 38 1/3 = 30 5/6 - 38 2/6 = - (38 2/6 - 30 5/6) = - (37 8/6 - 30 5/6) =

= - 7 3/6 = - 7 1/2 = - 7,5

Пояснения:

1/3 = 4/12 - доп. множ. 4

1/4 = 3/12 - доп. множ. 3

9 7/12 = (9*12+7) / 12 = 115/12

0,25 = 25/100 = 1/4 - сократили на 25

3/6 = 1/2 - сократили на 3

1/2 = 5/10 = 0,5