Question : A boat covers a distance of 72 km downstream in 6 hours, while it takes 12 hours to cover the same distance upstream. What is the speed of the boat in still water?
Option 1: 6 km/hr
Option 2: 9 km/hr
Option 3: 10 km/hr
Option 4: 8 km/hr
Correct Answer: 9 km/hr
Solution :
The speed of the boat in still water can be calculated using the speeds of the boat downstream and upstream.
$\text{Speed} = \frac{\text{Distance}}{\text{Time}}$
The speed of the boat downstream (with the current) is the distance divided by the time, which is
$\frac{72 }{6 }$ = 12 km/hr
The speed of the boat upstream (against the current) is also the distance divided by the time, which is $\frac{72 }{12 }$ = 6 km/hr
The speed of the boat in still water is the average of the downstream and upstream speeds, which is $\frac{12 + 6 }{2}$ = 9 km/hr
Hence, the correct answer is 9 km/hr.
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