ba kho A,B,C chua mot so gao . nguoi ta nhap vao kho A them 1/7 so gao cua kho do , xuat o kho B di 1/9 so gao o kho do , xuat o kho C di 2/7 so gao o kho do . kghi do so gao o ba kho bang nhau . tinh so gao o moi kho luc dau , biet rang kho B chua nhieu hon kho A 20 ta gao