21 thoughts on “A Puzzle of Knights

    • Again, let us see if there is a pattern. We need a minimum of 2 people of course. Let’s try….
      2 – 2
      3 – 1
      4 – 3
      5 – 5
      6 – 1
      7 – 3
      8 – 5
      9 – 7
      10 – 9
      11 – 11
      12 – 1
      13 – 3

      So do you see the pattern? Excepting the first case of 2 people, there is a clear pattern… Now I am sure you can figure out the rest from here…:)


    • No simple solution in either of these two cases. You can try for small numbers and check if a pattern emerges, but the pattern turns out to be fairly complex in both the cases you mentioned….the latter case, maybe something in bases systems would be feasible, would have to think about it.


  1. also what difference it will make when they are not removed continuously but at one time then started again ? for example in a count of 2000 number every 7 number is removed in every stage , what will be the last digit to be removed ? plz explain procedure

  2. Very nasty, Gaurav. For 3 or 4 you could still hope to derive a kind of pattern by trying it for small numbers; for 10 we would have to do a lot of trials before a pattern would emerge (if any). Thus it would be an exercise for a computer program and not for a manual effort. Consequently, you could safely guarantee that it would be unlikely to come in a test/interview.


  3. sir, in 1st question in 1st pass,
    1,3,5,7,9… left
    in second pass and in third pass also you started eliminating from 2nd no. in the row, then why did you chose 9 in 4th pass, shouldn’t it again be 1,17,25.. in 4th pass? and because the trick is also based on it. i got stuck here..

  4. Because in the first 2 passes the last person eliminated was the last person left (#300 and #299 respectively). But in the third pass the last person eliminated was 293, so two steps further from there will be 297 (remains) and 1 (eliminated), i.e. 1 will have to be eliminated at the beginning of the 4th pass. I am not starting each pass from 1 again, it is a continuous pass as already explained in an earlier comment.


  5. so can we conclude, that it is in the following a pattern of removing even terms(2nd, 4th, 6th, 8th..) in 1st three passes, odd ones in the next three passes and then evens and odds and so on in the gap of three passes?

  6. sir,
    when number of people are 4 first pass
    second pass
    1(eliminated), #3 is left out?
    could you please explain me how #1 was left as per your sol.

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