Three friends Pradeep, Suresh and Subodh workin the same office. During an extended weekend they decided to go together on a family trip to Corbett National Park. They started from office in their own car but at different time and travelled in the same direction at speeds of 50 km/hr, 60 km/hr and 75 km/hr respectively. Suresh and Subodh overtook Pradeep at the same point. If Suresh started 90 minutes after Pradeep, how many minutes after Pradeep did Subodh start from the office?
Explanation:
Consider the instance when Suresh just starts from the office. Distance that Pradeep has already covered in that time = 50*1.5 = 75 km Now, by concept of relative velocity, time taken by Suresh to just overtake Pradeep = 75/(60-50) = 7.5 hours Hence, the point of overtaking on the route is = 60*7.5 = 450 km from the office Subodh also overtakes Pradeep at the same point. Pradeep covers this 450 km distance in 9 hours. Subodh can cover this 450 km in 6 hours. Hence, Subodh can leave 9 - 6 = 3 hours after Pradeep does.
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