Mở cùng 1 lúc 1 vòi nước chảy vào bể và 1 vòi tháo nước ra khỏi bể thì trong 7 giờ số nước trong bể là 0,5 bể. Nếu mở vòi nước chảy vào trong 5 giờ và mở vòi tháo nước ra trong 6 giờ thì nước trong bể là 0,25 bể . Hỏi nếu mỗi vòi chảy 1 mình thì vòi 1 chảy đầy bể trong bao lâu? Vòi 2 tháo hết nước trong bể sau bao lâu ?

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