P and Q walk around a circular track. They start at 9 A.M. from the same point in the opposite directions. P and Q walk at a speed of 3 rounds per hour and 5 rounds per hour respectively. How many times shall they cross each other before 11.31 A.M.
Solution: Relative speed = (3 + 5) = 8 rounds per hour.
So, they cross each other 8 times in an hour and 4 times in half an hour.
Hence, they cross each other 20 times in 2.5(11.31 - 9.00) hours means before 11.31 A.M.
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