gs1medium
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?
- A.After 11 hours
- B.After 21 hours
- C.After 22 hours
- D.After 33 hours
▶ Answer & Explanation
Correct answer: C. After 22 hours
To meet at the starting point, each man must complete an integer number of laps. The time taken by each man to complete one lap is calculated by dividing the track length by their speed. The time they will meet again at the starting point is the Least Common Multiple (LCM) of their individual lap times. Man 1 takes 11/4 hours, Man 2 takes 11/5.5 = 2 hours, and Man 3 takes 11/8 hours. The LCM of 11/4, 2, and 11/8 is 22 hours.
Source: UPSC gs1 2010