Khi tang them 10 nguoi thi so nguoidao muong la : 30+10 = 40 ( nguoi)
Goi x la thoi gian de 40 nguoi dao xong con muong do. Do thoi gian va so luong nguoi ti le nghich nen:
30.8 = 40.x => x = 30.8:40 = 6
Vay: Neu tang them 10 nguoi thi dao xong con muong do mat het 6 ngay