Một thuyền máy dự định đi xuôi dòng từ A đến B rồi lại quay về Biết vận tốc của thuyền so với nước yên lặng là 15km/h , vận tốc của nước so với bờ là 3km/h , AB dài 18km a ) Tính thời gian chuyển động của thuyền b ) Tuy nhiên , trên đường quay về A , thuyền bị hỏng máy và sau 24 phút thì sửa xong . Tính thời gian chuyển động của thuyền

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