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Imagine we have a ruler on which just numbers 0 and 2 and 5 are marked and the rest numbers are erased. How could we draw a 6 cm line by this ruler?

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    $\begingroup$ Is this your own puzzle or did you find somewhere else? If so, kindly provide the source. $\endgroup$
    – Ak.
    Jan 5 at 12:12
  • $\begingroup$ I found this somewhere else but I don't know the main source $\endgroup$
    – Rahim
    Jan 5 at 12:13
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    $\begingroup$ Hi Rahim. Where was this 'somewhere else', please? All puzzles from elsewhere do need to have a source stated, even if you don't know the very first place it was published, otherwise it could fall foul of our plagiarism policy... Thanks :) $\endgroup$
    – Stiv
    Jan 5 at 12:33
  • $\begingroup$ Our school gave us this puzzle written on a piece of paper. I think I solved this. First I draw a 5 cm line then I marked 4 on that then I put the 0 mark of the ruler on 4 on the line and then I added a 2cm line to my previeus line ! $\endgroup$
    – Rahim
    Jan 5 at 12:38
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This solution seems to be a bit too simple:

Draw from 2 to 5 (which is 3 cm long). Shift the ruler 3cm to the right so that the 2-mark is at the end of your line, and again draw from 2 to 5 to extend your line by another 3cm.

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  • $\begingroup$ @msh210 You do have to keep the ruler parallel to the line you have already drawn, but as you have the part of the ruler between the 0 and 2 markings along the drawn line, that is no problem in practice. If you must do it perfectly, you need to put a second pencil at about the half-way point so that you can then slide the ruler along both pencils. $\endgroup$ Jan 5 at 14:22
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First draw 5 cm, back up 2 (now you have 3 cm marked), do the same again. Now you have 6 cm marked.

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