A man travels from A to B a 39 km distance with the speed of 15 km/hr and from B to C a 52 km distance at the speed of 18 km/hr. Find the average speed (in km/hr) of whole journey.

16\(\frac{11}{19}\)

Time taken from A to B = \(\frac{39}{15}\) = \(\frac{13}{5}\) hrs

Time taken from B to C = \(\frac{52}{18}\) = \(\frac{26}{9}\) hrs

Average speed = \(\frac{Total\;distance}{total\;time}\) = \(\frac{39 + 52}{\frac{13}{5} + \frac{26}{9}}\)

                        = 16\(\frac{11}{19}\) km/hr