Two-fifth of a journey is covered at a speed of 45 km/h, and the remaining distance is covered at the rate of 63 km/h. The average speed for the whole journey (in km/h, rounded off to the nearest integer) is:

Correct option is C

Let the total distance be 5km

In first part, distance covered = 5× $$\frac{2}{5}$$ = 2 km

Remaining Distance = 5-2 = 3 km

Average Speed = $$\frac{Total Distance}{Totaltime }= \frac{5}{\frac{2}{45}+\frac{3}{63}}$$ = $$= \frac{5×45×63}{261}$$ = 54 km/hr