1.our friends were thought by us all time
2.he will be operated by the doctor in a week
3.the pupil's parents were sent for by the teacher
4.the newspaper was looked for by them everywhere
5.nobody was slept in the bed
6. the telegram was asked for by the neghbor
7. the lecturer was listened to by everybody with great attention
8. the freshman was laughted at by the senior students
9. the headmistress was spoken by the group yesterday
10. their babies were looked after by the young mothers with great care
1) 2(x-3)=4
2x-6=4
2x=4+6
2x=10
x=5
1)3(x-4)=5x
3x-12=5x
3x-5x=12
-2x=12
x= -6
2) -(4x-3)=-x
-4x+3=-x
-4x+x=-3
-3x=-3
x=1
2) -(5x-8)=-x
-5x+8=-x
-5x+x=-8
-4x=-8
x=2
3) -4(х+5)=-16
-4x-20=-16
-4x=-16+20
-4x=4
x=-1
3) -5(x+2)=-15
-5x-10=-15
-5x=-15+10
-5x=-5
x=1
4)3(х+7)=2(х-8)
3x+21=2x-16
3x-2x=-16-21
x=-37
4) 7(х-2)=6(х+1)
7x-14=6x+6
7x-6x=6+14
x=20
5) 4(-х+7)=-(х+2)
-4x+28=-x-2
-4x+x=-2-28
-3x=-30
x=10
5) 3(х+2)=-(х-8)
3x+6=-x+8
3x+x=8-6
4x=2
x= 0,5
6) -3(2-х)=4(х+9)
-6+3x=4x+36
3x-4x=36+6
-x=42
x=-42
6) -5(7-х)=6(х+2)
-35+5x=6x+12
5x-6x=12+35
-x=47
x=-47
200 г - 100%
х г - 70%
х = 200*70:100 = 140 г чистой кислоты
2) Пусть надо добавить у г воды, тогда
140 г -7%
200+у - 100%
(200+у)*7 = 140*100
1400 +7у = 14000
7у= 14000-1400
7у= 12600
у= 12600:7
у=1800
Итак, надо добавить 1800 грамм воды