UPSC Prelims 2010·GS1·geography·general geography

Three men start together to travel the same way around a circular track of 11 km. Their speeds are 4, 5.5 and 8 kmph respectively. When will they meet at the starting point for the first time?

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Last updated 8 Jul 2026, 4:39 pm IST
  1. AAfter 11 hours
  2. BAfter 21 hours
  3. CAfter 22 hours.Correct
  4. DAfter 33 hours

Explanation

To find when the three men will meet at the starting point for the first time, we need to calculate the time each person takes to complete one full lap and then find the Least Common Multiple (LCM) of those times.

Step 1: Calculate the time taken for one lap by each person using the formula Time = Distance divided by Speed. Man 1: 11 / 4 hours. Man 2: 11 / 5.5 hours (which is 110 / 55, or 2 hours). Man 3: 11 / 8 hours.

Step 2: Find the LCM of these three time intervals: 11/4, 2/1, and 11/8. To find the LCM of fractions, you take the LCM of the numerators and divide it by the Highest Common Factor (HCF) of the denominators. LCM of numerators (11, 2, 11) = 22. HCF of denominators (4, 1, 8) = 1.

Step 3: Calculate the final result. 22 divided by 1 = 22.

Therefore, they will meet at the starting point for the first time after 22 hours. The correct option is C.

geography: Three men start together to travel the same way around a circular track of 11 km. Their speeds are 4, 5.5 and 8 kmph res
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