Two-thirds of a certain distance was covered at the speed of 45 km/h, one-fourth at the speed of 60 km/h and the rest at the speed of 75 km/h. Find the average speed per hour for the whole journey. (correct to 2 decimal places)

Solution (By Examveda Team)

$$\eqalign{ & {\text{Let distance}} = 1200{\text{ km}} \cr & {\text{Average speed}} = \frac{{1200}}{{\frac{{800}}{{45}} + \frac{{300}}{{60}} + \frac{{100}}{{75}}}} \cr & = \frac{{1200}}{{\frac{{160}}{9} + 5 + \frac{4}{3}}} \cr & = \frac{{1200 \times 9}}{{217}} \cr & = 49.77{\text{ km/h}} \cr} $$