The cruise ship

The cruise ship has a speed of 12 km/h at a calm surface. When we sail 45 km along the river and 45 km back, it took us exactly 8 hours. Which (constant) speed of flow of the river?

Correct result:

v =  3 km/h


45=t1(12+v) 45=(8t1) (12v) t1=45/(12+v) 45=(845/(12+v)) (12v)  45(12+v)=(8(12+v)45)(12v)  45 (12+v)=(8 (12+v)45) (12v) 8v272=0  a=8;b=0;c=72 D=b24ac=0248(72)=2304 D>0  v1,2=b±D2a=±230416 v1,2=±4816 v1,2=±3 v1=3 v2=3   Factored form of the equation:  8(v3)(v+3)=0  v>0 v=v1=3=3 km/h t1=45/(12+v)=45/(12+3)=3 h t2=45/(12v)=45/(123)=5 h

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