A car travelled distances of 10 km, 20 km and 30 km at speeds of 30 km/h, 40 km/h and 60 km/h, respectively. The average speed of the car is:

45 km/h

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

Distance = Speed × Time

Total distance = 10 + 20 + 30= 60 km

Total time =   \(\frac{10 }{30 }\) +  \(\frac{20 }{40 }\) + \(\frac{30 }{60}\) =    \(\frac{1 }{3 }\) +  1

= \(\frac{4 }{3 }\)

Average speed =   \(\frac{60 × 3  }{4 }\) = 45 km/h