Suresh plans a trip from city A to city B which are ‘x’ km apart and returning to city A. There are two light traffic zones of 25 km length each where he goes at a speed of 20 km/hr and returns at a speed of 25 km/hr. There are two heavy traffic zones of 35 km length each where he goes with a speed of 14 km/hr and returns at a speed of 21 km/ hr. For other part of the journey he maintains his speed at 90 km/hr while going and 60 km/hr while returning. If it took 2 hrs extra to go to city B from city A than to return from city B to city A, what is the approximate average speed with he was moving during his return journey (in km/hr)?
Suresh plans a trip from city A to city B which are ‘x’ km apart and returning to city A. There are two light traffic zones of 25 km length each where he goes at a speed of 20 km/hr and returns at a speed of 25 km/hr. There are two heavy traffic zones of 35 km length each where he goes with a speed of 14 km/hr and returns at a speed of 21 km/ hr. For other part of the journey he maintains his speed at 90 km/hr while going and 60 km/hr while returning. If it took 2 hrs extra to go to city B from city A than to return from city B to city A, what is the approximate average speed with he was moving during his return journey (in km/hr)? Correct Answer 26
For the journey from city A to city B
Time = Speed/Distance
Total time taken = Time taken in light traffic zones + Time taken is heavy traffic zones + Time taken to cover rest of the distance
Ta = 2 × 25/20 + 2 × 35/14 + (x - 120)/90 = 7.5 + (x - 120)/90
For journey from city B to city A
Tb = 2 × 25/25 + 2 × 35/21 + (x - 120)/60 = 5.333 + (x - 120)/60
Given Ta - Tb = 2
0.167 = (x - 120)/60 - (x - 120)/90
0.167 = {3(x - 120) - 2(x - 120)}/180
⇒ x = 150 km
Time taken in reverse journey = 5.333 + (150 - 120)/60
= 5.833 hrs
Average speed = 150/5.8333 ≈ 26 km/hr