A bullock cart has to cover a distance of 120 km in 15 hours. If it covers half of the journey in $$\frac{3}{5}$$th time, the second to cover the remaining distance in the time left has to be :

Total distance = 120 km
Total time = 15 hours
He covers half of the journey in $$\frac{3}{5}$$th of the time
= 15 × $$\frac{3}{5}$$ hours
= 9 hours
Now, remaining distance :
= (120 - 60) km
= 60 km
And, remaining time :
= (15 - 9) hours
= 6 hours
Average speed to cover a distance of 60 km will be :
$$\eqalign{ & = \frac{{60\,\,{\text{km}}}}{{6\,\,{\text{hour}}}} = 10\,\,{\text{km/hr}} \cr & \left\{ {{\text{Speed}} = \frac{{{\text{Distance}}}}{{{\text{Time}}}}} \right\} \cr} $$