UPSC Prelims 2004·GS1·geography·general geography

A and B start from the same point and in the same direction at 7 a.m. to walk around a rectangular field 400 m x 300 m. A and B walk at the rate of 3 km/hr and 2.5 km/hr respectively. How many times shall they cross each other if they continue to walk till 12:30 p.m.?

Dalvoy logo
Reviewed by Dalvoy
UPSC Civil Services preparation
Last updated 23 May 2026, 3:31 pm IST
  1. ANot even once
  2. BOnceCorrect
  3. CTwice
  4. DThrice

Explanation

The perimeter of the rectangular field is 2 times (400 + 300) = 1400 meters = 1.4 kilometres. Since A and B walk in the same direction, the relative speed is 3 - 2.5 = 0.5 km/hr. For A to overtake B (cross at the starting point again), A must gain one full perimeter over B. Time required = 1.4 km / 0.5 km/hr = 2.8 hours. Total walking time from 7 a.m. to 12:30 p.m. is 5.5 hours. First crossing occurs at 2.8 hours. Second crossing would occur at 5.6 hours, which exceeds the total walking time of 5.5 hours. Therefore, they cross each other exactly once.
geography: A and B start from the same point and in the same direction at 7 a.m. to walk around a rectangular field 400 m x 300 m.
ShareWhatsAppXTelegram

Related questions

More UPSC Prelims practice from the same subject and topic.