Question : A boat goes a certain distance at 30 km/hr and comes back the same distance at 60 km/hr. What is the average speed (in km/hr) for the total journey?
Option 1: 45 km/hr
Option 2: 50 km/hr
Option 3: 40 km/hr
Option 4: 35 km/hr
Correct Answer: 40 km/hr
Solution :
Given: The speed of the boat is 30 km/hr and 60 km/hr for the same distance.
So, average speed = $\frac{2xy}{x+y}$, where $x$ and $y$ are two given speeds of the boat (for the same distance).
Putting the values $x$ = 30 and $y$ = 60, we get,
$\therefore$ Average speed = $\frac{2×30×60}{30+60}$ = $\frac{3600}{90}$ = 40 km/hr
Hence, the correct answer is 40 km/hr.
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