A car covers 25% of a distance with the speed of 20 km/hr and next 25% of the distance with the speed of 40 km/hr and remaining distance with the speed of 50 km/hr, find the average speed of car in the whole journey is.?

Option 4 : 800/23 km/hr

Given,

Car covers 25% of the distance with the speed of = 20 km / hr

Car covers next 25% of the distance with the speed of = 40 km / hr

Rest distance covers with the speed of = 50 km / hr

Formula:

Average speed = Total distance / total time

Calculation:

Let total distance be 400 km.

25% of the total distance = 400 × (25 / 100) = 100 km

25% of the total distance = 400 × (25 / 100) = 100 km

Remaining distance = 100% - 25% - 25% = 50%

50% of the distance = 400 × (50 / 100) = 200 km

Time taken by car to cover 100 km with the speed of 20 km / hr = 100 / 20 = 5 hrs

Time taken by car to cover 100 km with the speed of 40 km / hr = 100 / 40 = 2.5 hrs

Time taken by car to cover 200 km with the speed of 50 km / hr = 200 / 50 = 4 hrs

Total time = 5 + 2.5 + 4 = 11.5 hrs

∴ Average speed of car = 400 / 11.5 = 800 / 23 km / hr