The speed of a river current is 5 km/h.A boat takes the same time to travel 15 km downstram.Find the boat's speed in still water
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Let the speed of boat in still water be x km/h
Now
In Upstream, we know that
Speed of Boat = Speed of boat in still water - speed of river current
∴ Speed of boat in upstream = x - 5
Distance in upstream = 8 km
∴ Time taken in upstream = 8/(x-5) [Time = distance/speed] --- ( i )
In Downstream
Speed of boat = Speed of boat in still water + speed of river current
∴ Speed of boat in downstream = x + 5
Distance = 12 km
∴ Time taken in downstream = 12/(x + 5) --- ( ii )
According to question
Time taken in upstream = time taken in downstream
∴ Eq ( i ) = Eq ( ii )

8 ( x + 5) = 12 ( x - 5 )
8x + 40 = 12x - 60
4x = 100
x = 25
∴ Speed of boat in still water is 25km/h
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