Vận tốc của xuồng máy đó trong 1 giờ là :50 x 60 = 3000 ( m/giờ )
Đổi : 3000 m = 3 km
Trên cùng một quãng đường , vận tốc và thời gian là hai đại lượng tỉ lệ nghịch với nhau .
Tỉ lệ thời gian xuôi dòng và ngược dòng là : \(\frac{4}{6}=\frac{2}{3}\)
Vậy tỉ lệ vận tốc xuôi dòng và vận tốc ngược dòng là : \(\frac{3}{2}\).
Hiệu vận tốc là : 3 x 2 = 6 ( km/giờ )
Hiệu số phần bằng nhau là : 3 - 2 = 1 ( phần )
Vận tốc ngược dòng là : 6 : 1 x 2 = 12 ( km/giờ )
Quãng sông AB dài : 12 x 6 = 72 ( km )
Đ/S : ...
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