Civil Services Examination · Question 37
P and Q walk along a circular track. They start at 5:00 a.m. from the same point in opposite directions. P walks at an average speed of 5 rounds per hour and Q walks at an average speed of 3 rounds per hour. How many times will they cross each other between 5:20 a.m. and 7:00 a.m.?
Show answer & explanation
Answer: (B) 13
Explanation
Relative speed 8 rounds/hour, so they meet every 7.5 minutes (5:07:30, 5:15, 5:22:30, ...). Between 5:20 and 7:00 (excluding the meeting exactly at 7:00) there are 13 crossings. (Answer as per the official UPSC answer key.)