November 2014

Going round in circles once again

Sports ground

In the October 2013 teaser (Going round in circles) I had narrated how the sight of a sports complex had brought back fond memories. I had told you how my friend and I had started walking in opposite directions, and had wanted to know how many times did my friend and I pass each other during the one-and-half hour walk.

I was wondering how many times we would pass each other had we been walking in the same direction instead of in the opposite direction. Can you help me determine this?

Let me put the question once again in the proper perspective:

My friend and I went to the sports complex after many years. The sight brought back many happy memories. In our younger days, the complex used to be our favourite haunt and we used to begin the day with a morning jog.

We thought of reliving those good old days. We decided to walk. We decided to walk in the same direction. It was a circular track. We started walking at exactly at 8 am. Now, I am slower than my friend. I could walk at a speed of two rounds per hour while my friend completed three rounds per hour. We stopped walking at 9.30 am - we, therefore, walked continuously for one-and-half hours.

Can you tell how many times did my friend and I pass each other during the course of the walk?

Click here for the solution

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  • Birla Institute of Technology, Ranchi -
  • Central Institute of Fisheries Nautical and Engineering Training -
  • Indian Institute of Information Technology, Allahabad (Deemed University) -
  • Central Marine Fisheries Research Institute, Kochi -
  • Tata Institute of Social Sciences, Mumbai -

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