Bai 1 Ba lop 7a,7b,7c co 105 hoc sinh tham gia ngoai khoa. Tinh so hoc sinh tham gia hoat dong ngoai khoa cua moi lop biet rang so hoc sinh tham quan ngoai khoa cua cac lop tuong ung ty le voi 5,6,7. Bai 2 : Tim x : a) 72x +(-3,7x)-2,7=7,8 b)\(\frac{x}{3}=\frac{2}{15}\) c) (x+3)\(^2\)= -27 d) |x+2|+2,1=5,7 e) (2x-1)\(^2\)=16 f) x+\(\frac{5}{4}\)= \(\frac{3}{2}\)