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Question

A motorboat that travels with a speed of 20 km/hour in still water has traveled 20 km against the current and 180 km with the current, having spent 8 hours on the entire trip. Find the speed of the current of the river.

A motorboat that travels with a speed of 20 km/hour in still water has traveled 20 km against the current and 180 km with the current, having spent 8 hours on the entire trip. Find the speed of the current of the river.

Answer 1

Let B = Speed of Boat = 20km/hr

Let C = Speed of Current.

 

Distance travelled = Speed * Time.

 

When traveling against the current the net speed is = (B-C)

Let t1 = time travelled against the current.

 

Then 20 = (B-C) * t1 

 

When traveling in the direction of the current, the net speed is = (B+C)

Let t2 = time travelled in the direction of current.

Then 180 = (B+C) * t2

 

The total time travelled is 8 hrs 

Therefore t1 + t2 = 8

From above we can state that 

20/ (B-C)  + 180/ (B+C)  = 8

 

B is known quantity. Solve the above to find C.