Question : A boat running downstream covers a distance of 20 km in 2 hours, while it covers the same distance upstream in 5 hours. Then, the speed of the boat in still water is:
Option 1: 7 km/hr
Option 2: 8 km/hr
Option 3: 9 km/hr
Option 4: 10 km/hr
Correct Answer: 7 km/hr
Solution :
Given: A boat running downstream covers a distance of 20 km in 2 hours, while it covers the same distance upstream in 5 hours.
Downstream speed = $\frac{20}{2}=10$ km/hr
Upstream speed = $\frac{20}{5}=4$ km/hr
By applying the formula, we have,
The speed of the boat in still water = $\frac{\text{Downstream speed}+\text{Upstream speed}}{2}$
⇒ The speed of the boat in still water = $\frac{10+4}{2}=7$ km/hr
Hence, the correct answer is 7 km/hr.
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