3.A
4.C
Bài2.3
II-Tự luận
Bài1:
1200:{780:[1000-(250+35.14)]}+2
=1200:{780:[1000-(250+490)]}+2
=1200:{780:[1000-740]}+2
=1200:{780:260}+2
=1200:3+3
=400+2
=402
Bài2:
a,192-3.(x+1)=84
3(x+1)=192-84
3(x+1)=108
x+1=108:3
x+1=36
x=36-1
x=35
Vậy x=35