Question : The speed of a boat in still water is 9 km/hr and the speed of the stream is 6 km/hr. If a man goes a distance of 45 km against the stream and comes back to the starting point, then what is the total time taken by him?
Option 1: 20 hours
Option 2: 30 hours
Option 3: 24 hours
Option 4: 18 hours
Correct Answer: 18 hours
Solution :
The upstream speed = 9 – 6 = 3 km/hr
The downstream speed = 9 + 6 = 15 km/hr
The time taken to travel 45 km upstream = $\frac{45}{3}$ = 15 hours
The time taken to travel 45 km downstream = $\frac{45}{15}$ = 3 hours
Therefore, the total time taken by the man to go 45 km against the stream and come back to the starting point is 15 + 3 = 18 hours
Hence, the correct answer is 18 hours.
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