Question

the speed of the boat in still water is 8km/hr.If it takes the same time in going 20km downstream as it takes in going 12km upstream,find the speed of the water

Answer 1

Let the speed of water in the river be x km/hr
Speed of boat upstream = (8 – x) km/hr
Speed of boat downstream = (8 + x) km/hr
Distance travelled downstream = 20 km
Recall that time taken = (Distance)/(Speed)
Time taken to travel downstream = 20/(8 + x)
Distance travelled upstream = 12 km
Time taken to travel upstream = 12/(8 – x)
Given time taken to travel downstream = time taken to travel upstream

Thus speed of water in the river is 2 km/hr.

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clear
Let the speed of water in the river be x km/hr
Speed of boat upstream = (8 – x) km/hr
Speed of boat downstream = (8 + x) km/hr
Distance travelled downstream = 20 km
Recall that time taken = (Distance)/(Speed)
Time taken to travel downstream = 20/(8 + x)
Distance travelled upstream = 12 km
Time taken to travel upstream = 12/(8 – x)
Given time taken to travel downstream = time taken to travel upstream

Thus speed of water in the river is 2 km/h