Thể tích hồ là :
4 x 2 x 0,8 = 6,4 ( m3 )
Trong hồ đang có số nước là :
6,4 x 3/4 = 4,8 ( l )
Phải đổ thêm số nước là :
6,4 - 4,8 = 1,6 ( l )
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