Question : A woman drives a car. During her journey, she travels 20 minutes at a speed of 60 km/hr, another 30 minutes at a speed of 40 km/hr and 1 hour at a speed of 50 km/hr. The average speed of the car is:
Option 1: $\frac{540}{11}$ km/hr
Option 2: $\frac{630}{11}$ km/hr
Option 3: $\frac{100}{11}$ km/hr
Option 4: $\frac{90}{11}$ km/hr
Correct Answer: $\frac{540}{11}$ km/hr
Solution :
Total distance = $\frac{20}{60}×60 + \frac{30}{60}×40 + 1×50= 20 + 20 + 50= 90$ km
Total time = $\frac{20}{60} + \frac{30}{60} + 1= \frac{2+3+6}{6}= \frac{11}{6}$ hr
Average speed = $\frac{\text{Total distance}}{\text{Total time}}= \frac{90}{\frac{11}{6}}= \frac{540}{11}$
Hence, the correct answer is $\frac{540}{11}$ km/hr.
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