a man can row a boat at 4.5 km/hr in still water to a certain upstream point and can row back to the starting point in a river flowing with 1.5 km/hr. The average speed during the total journey is :
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Answer: The average speed during the whole journey would be 2.25 km/h.
Step-by-step explanation:
Average speed= total distance coverd/total time taken
Suppose, distance between one end to other= d km
Total distance covered= 2d
Time taken during journey in still water= d/4.5
Time taken during upstream journey= d/1.5
Total time taken during the whole journey= d/4.5+d/1.5
Average speed of the man= 2d/(d/4.5+d/1.5)= 2/(1/4.5+1/1.5)
Average speed of the man= 2*1.5*4.5/(1.5+4.5)= 2.25 km/h
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