What happens to the two strings - of the logo of G20 Summit enter image description here(currently happening in Germany)-if pulled either side (in opposite directions, away from the center) at the same time ?

Your options are:

(a) They separate out as two different strings
(b) They get tied to each other- as a knot
(c) They just hold each other by a single strand
(d) None of the above

Also explain why /how.


2 Answers 2


Assuming the ropes are flexible and have a low coefficient of friction, it depends on which 'sides' you pull. Labeling the 4 ends A, B, C, D (and the mid-points AC and BD, then, if you pull two ends (or an end and a middle):

Pulling A and B or A and D or A and BD or C and B or C and D or C and BD or B and AC or D and AC, or AB and CD the ropes will separate into two length. Whereas pulling A and C or B and D, one rope will straighten and the other will end up hanging in a twisted loop around it (see figure).

If you pull three ends and/or middles:

Pulling on three points on one rope (for example A C and AC) won't undo the 'knot', but pulling on any two points on one rope and a third point on the other rope will separate them into two lengths.

...and if you pull all four ends

Pulling on all four ends will tighten the knot.

Picture showing pulling on ends A and C

enter image description here

If there is friction in the ropes, or if the hidden ends are not open, then all bets are off.

  • $\begingroup$ Wow ! Good one !! @Penguino, your answer is much clearer and to the point (I mean in terms of the options I have provided for this puzzle) are relevant straight to the question. I should definitely accept this as the most comprehensive and apt answer for my question than the previous ones. Thanks. $\endgroup$ Jul 14, 2017 at 15:26

I'm not sure if this is actually a puzzle more than a general knowledge question but:

The G20 Summit Logo is actually a Reef Knot, so it you pull the 'ends' tight it is the knot (b), if you pull the 'loops' from the centre if would come loose and providing the strings are cut as shown in the logo, they would separate out as two strings (a).

The knot looks like this:

enter image description here

  • $\begingroup$ Yeah, I'd agree. A picture of a reef knot and asking what happens when you pull the ends isn't really a puzzle... $\endgroup$
    – Chris
    Jul 12, 2017 at 10:02
  • $\begingroup$ Good information @BreakingMyself. Informative. I am an amateur in stackexchange. So kindly bear with me. $\endgroup$ Jul 12, 2017 at 10:15
  • $\begingroup$ Well Chris, I am getting to understand the kind of jargon / type of puzzles being asked. So please cooperate :-). $\endgroup$ Jul 12, 2017 at 10:16
  • 1
    $\begingroup$ @ChandrasekharK I'd recommend reading through a few posts and checking the tag descriptions here: puzzling.stackexchange.com/tags for different puzzles and topics shared on the site. I'm relatively new myself so don't worry about it :) $\endgroup$ Jul 12, 2017 at 10:25

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