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

Options

A. `(30+25+50)/(3)`
B. `((a)/(30)+(1)/(25)+(1)/(50))/(3)`
C. `(3)/((1)/(30)+(1)/(25)+(1)/(50))`
D. None of these

Answer

C

Explanation

Average speed`=(120+120+120)/((150)/(30)+(120)/(25)+(120)/(50))`
`=(3)/((1)/(30)+(1)/(25)+(1)/(50)) "km"//"hour"`