A train covers 20 km, 30 km, 60 km and 90 km at speeds of 10 km/h, 15 km/h, 12 km/h and 18 km/h respectively. The average speed of the train for the total journey is:

\(\frac{100}{7}\)

Total distance = 20 + 30 + 60 + 90 = 200

Total time = \(\frac{20}{10}\) + \(\frac{30}{15}\) + \(\frac{60}{12}\) +\(\frac{90}{18}\)

                = 2 + 2 + 5 + 5

                = 14

Average speed = \(\frac{Total\;distance}{Total\;time}\)

                      = \(\frac{200}{14}\)

                      = \(\frac{100}{7}\)