Question : During a journey of 120 km, Rahi drives the first 60 km at the speed of 60 km/hr, the next 30 km at 60 km/hr and the remaining 30 km at the speed of 30 km/hr. Determine the average speed.
Option 1: 48 km/hr
Option 2: 33.33 km/hr
Option 3: 50 km/hr
Option 4: 40 km/hr
Correct Answer: 48 km/hr
Solution :
Rahi drives the first 60 km at the speed of 60 km/hr.
Time taken $=\frac{60}{60}=1$ hour
The next 30 km at 60 km/hr.
Time taken $=\frac{30}{60}=\frac{1}{2}=0.5$ hour
The remaining 30 km at the speed of 30 km/hr.
Time taken $=\frac{30}{30}=1$ hour
Total time taken = 1 + 0.5 + 1 = 2.5 hours
Total distance = 120 km
$\therefore\text{Average speed}=\frac{\text{Total distance}}{{\text{Total time}}}=\frac{120}{2.5}=48$ km/hr
Hence, the correct answer is 48 km/hr.
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