а) 4/5 = 3 :4Х б) 8/9 = 1/2Х
16Х = 15 16Х = 9
Х = 15/16 Х = 9/16
в) 27/40 = 18Х/25
720Х = 675
Х = 675/720
Х = 135 /144
3,9 - ( 5,81 - x ) = - 3 3/4
3,9 - 5,81 + x = - 3 3/4
- 1,91 + x = - 3 3/4
x = - 3,75 + 1,91
x = - 1,84
18:3=(12+6):3=4+2=6
21:3=(18+3):3=6+1=7
24:3=(18+6):3=6+2=8
27:3=(24+3):3=8+1=9