Delhi Police Constable Exam Model Paper 6

Given ,
Car covers $\frac{1}{4^{\mathit{t}\mathit{h}}}$ of a distance with the speed of 10 km/hr
Rest distance covers with the speed of 40 km/hr
Formula:
Average speed = Total distance/Total time
Calculation:
Let total distance be 160 km. (160 is assumed to make our calculation easy)
$\frac{1}{4^{\mathit{t}\mathit{h}}}$ of total distance = (1 / 4) × 160 = 40 km
Remaining distance = 160 - 40 = 120 km
Time taken by car to cover 40 km distance with a speed of 10 km/hr = 40/10 = 4 hrs
Time taken by car to cover 120 km distance with a speed of 40 km/hr = 120/40 = 3 hrs
Total time = 4 + 3 = 7 hrs
∴ Average speed = 160/7 km/hr