A bus goes to Mumbai from Delhi at the speed of 60 km/h for 60% of the journey, and covers the remaining part of its journey at the speed of 70 km/h. What is the average speed of the bus (in km/h) during the entire journey under consideration?

64

Average Speed = \(\frac{Total \;Distance\; traveled }{Total\; Time \;Taken }\)

Let the Distance from Mumbai to Delhi = 100D km

60% of distance = 60% of 100D = 60D

Time = \(\frac{60D}{60}\) = D hours

Remaining Distance = 100D - 60D = 40D

Time taken = \(\frac{40D}{70}\)  = \(\frac{4D}{7}\) 

Total Time = D + \(\frac{4D}{7}\)  = \(\frac{11D}{7}\) 

Average Speed = \(\frac{100D × 7 }{11D}\)

Average Speed = 63.63 km/h 

= 64 km/h   ( approx)