A person covers 30% of the distance from A to B at 10 km/h.  25% of the distance at 20 km/h and the rest at 15 km/h.  His average speed (in km/h) for the journey is?

13\(\frac{23}{29}\)

Avg. speed = \(\frac{Total\;distance}{Total\;Time}\) = \(\frac{100}{\frac{30}{10} + \frac{25}{20} + \frac{45}{15}}\)

= \(\frac{100}{3 + \frac{5}{4} + 3}\) = \(\frac{100 × 4}{29}\)

= 13\(\frac{23}{29}\) km/h