Question 31

The time taken by a boat to travel a distance downstream is half the time taken by it to travel the same distance upstream. What is the speed of the boat downstream if it travels 7.5 km upstream in 1 hour 30 minutes ? (in km/h)

Solution

Let the speed of boat in still water and speed of river be B km/hr and R km/hr respectively .

Speed of boat in downstream = B+ R km/hr

Speed of boat in upstream = B-R km/hr = $$\frac{7.5}{1.5}$$= 5km/hr

Let the same distance travelled in upstream and downstream be D km

So ,

$$\frac{D}{B-R}$$ =2× $$\frac{D}{B+R}$$

B+R = 10 km/hr

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