The boat

A boatman rows 2 km against the current in 40 minutes and returns to the same spot in 30 minutes. What is his rowing speed in still water?

Final Answer:

v =  3.5 km/h

Step-by-step explanation:

s=2 km t1​=40 min→ h=40:60  h=0.66667 h t2​=30 min→ h=30:60  h=0.5 h  s=(v−x)⋅ t1​ s=(v+x)⋅ t2​ 2=(v−x)⋅ 0.66666666666667 2=(v+x)⋅ 0.5  0.666667v−0.666667x=2 0.5v+0.5x=2  Row2−0.666666670.5​⋅ Row1→Row2 0.67v−0.67x=2 x=0.5  x=10.5​=0.5 v=0.666666672+0.66666666666667x​=0.666666672+0.66666667⋅ 0.5​=3.5=3.5 km/h  v=27​=3.5 x=21​≐0.5

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