Wise geek Posted May 23, 2015 Share Posted May 23, 2015 A and B walk around a circular track. They start at 8:00 am from the same point in opposite directions. A and B walk at a speed of 2 rounds per hour and 3 rounds per hour respectively. How many times shall they cross each other before 9:30 am.(Answer- 7) Quote Link to comment Share on other sites More sharing options...
Brent Hanneson Posted May 28, 2015 Share Posted May 28, 2015 A and B walk around a circular track. They start at 8:00 am from the same point in opposite directions. A and B walk at a speed of 2 rounds per hour and 3 rounds per hour respectively. How many times shall they cross each other before 9:30 am.(Answer- 7) Let's use some values to help us. Let's say that the CIRCUMFERENCE of the track = 1 mile So, if A completes 2 rounds (which is a total of 2 miles) per hour, then A is walking 2 miles per hour. Likewise, if B completes 3 rounds (which is a total of 3 miles) per hour, then B is walking 3 miles per hour. So, if A and B are walking towards each other, they are CLOSING THE GAP at a rate of 5 miles per hour (2 mph + 3 mph = 5 mph) Starting at 8:00am, A and B are essentially 1 mile apart (since they are walking in different directions). In other words, the GAP between them is 1 mile. NOTE: Time = distance/rate If the GAP is 1 mile, and the GAP closes at a rate of 5 miles per hour, then... Time until A and B meet = 1/5 hours = 12 minutes So, it takes 12 minutes until A and B pass each other for the first time. This means it will take another 12 minutes until they pass each other for the second time. And so on. In other words, they pass each other every 12 minutes So, how many times will they pass each other from 8am to 9:30am? This equals 90 minutes 90/12 = 7.something So, they will cross each other 7 times. Cheers, Brent Quote Link to comment Share on other sites More sharing options...
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