Question

An automobile driver travels from plane to a hill station 120 km distant at an average speed of 30 km per hour. He then makes the return trip at an average speed of 25 km per hour. He covers another 120 km distance on plane at an average speed of 50 km per hour. His average speed over the entire distance of 360 km will be

• A. $\frac{30 + 25 + 50}{3}$km/hr
• B. $(30,25,50)^{\frac{1}{3}}$
• C. $\frac{3}{\frac{1}{30} + \frac{1}{25} + \frac{1}{50}}$km/hr
• D. None of these

Answer 1

Answer: (C)

$\frac{3}{\frac{1}{30} + \frac{1}{25} + \frac{1}{50}}$km/hr

Answer 2

Average speed $=$ $\frac{120 + 120 + 120}{\frac{120}{30} + \frac{120}{25} + \frac{120}{50}}$

$= \frac{3}{\frac{1}{30} + \frac{1}{25} + \frac{1}{50}}km/hr$.