Question : A man travels 50 km at 25 km/hr, the next 40 km at 20 km/hr, and then 90 km at 15 km/hr. His average speed is:
Option 1: 18 km/hr
Option 2: 25 km/hr
Option 3: 20 km/hr
Option 4: 15 km/hr
Correct Answer: 18 km/hr
Solution :
Given:
A man travels the first 50 km at 25 km/hr, the next 40 km at 20 km/hr and the last 90 km at 15 km/hr.
Time taken to travel 50 km = $\frac{50}{25}$ = 2 hours
Time taken to travel 40 km = $\frac{40}{20}$ = 2 hours
Time taken to travel 90 km = $\frac{90}{15}$ = 6 hours
Total distance = (50 + 40 + 90) = 180 km
Total time = (2 + 2 + 6) = 10 hours
Average speed $=\frac{\text{Total distance}}{\text{Total time}}=\frac{180}{10}=$ 18 km/hr
Hence, the correct answer is 18 km/hr.
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