A distance of 320 km is traveled in three parts first 100 km at a speed of 20 km/hr, for the next 100 km it increases its speed by 25%, and for the last 120 km, it increases its speed further by 20%. Find the average speed of the whole journey. (approx.)
1
45 km/hr
2
25 km/hr
3
30 km/hr
4
64 km/hr
5
20 km/hr