Question : A person walks 10 km at a speed of 2.5 km/hr, then runs 10 km at a speed of 5 km/hr and then goes 30 km by bus at the speed of 30 km/hr. What is the average speed of the man?
Option 1: 9 km/hr
Option 2: 8.25 km/hr
Option 3: 7.14 km/hr
Option 4: 7 km/hr
Correct Answer: 7.14 km/hr
Solution :
Time taken to walk 10 km at a speed of 2.5 km/hr = $\frac{10}{2.5}$ = 4 hr
Time taken to run 10 km at a speed of 5 km/hr = $\frac{10}{5}$ = 2 hr
Time taken to go 30 km by bus at a speed of 30 km/hr = $\frac{30}{30}$ = 1 hr
Total time = 4 + 2 + 1 = 7 hr
Total distance = 10 + 10 + 30 = 50 km
Average speed = $\frac{\text{Total distance}}{\text{Total time}}$
= $\frac{50}{7}$
= 7.14 km/hr
Hence, the correct answer is 7.14 km/hr.
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