The above respondent has provided a number of sophisticated answers, which are simply amazing :)
Originally, I was thinking in another possible way: if we draw a line and divide it into twelve equal sections, then we need to first mark thirteen equally-distanced dots (including the starting and ending points of this line), and the seventh dot is located right at the half of that line. But then, comparing with the ones given from the first respondent, this suggestion is completely nothing.
Finally, why does this user keep raising so many questions in mathematics rather than questions in language aspects??