Is $1 : 7 = 1 / 8$ or is it $1/7$? In a certain (non-mathematical) Stack Exchange, when I wrote $n : m = n / m$ where $n$ and $m$ are positive integers, one of the moderators said "No! $n : m$ is usually the notation for "$n$ parts in $(n + m)$ parts vs. $m$ parts in $(n + m)$ parts, thus it means $n / (m + n)$." And many participants agreed with that and kept on saying I was wrong.
My question is...
Is there any background, educational say, that makes them that insistent? First I thought I would show them the definition of colon ideals to convince them of their false faith, but on second thought I concluded that would have made things worse.
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On having a look at the answer by dREaM, I think I have to add the context.
Someone asked to provide clarification (=translation) of certain passage from a fiction that runs like "the (average) physical capacity/ablility of a human kind is one-seventh of that of a vampire." As the original appeder asked if one-seventh = $1 : 7$, I said "yes, one-seventh $= 1 : 7 = 1 / 7$." Then came the frenzy.  
Thus I had no idea why the moderator brought in $8 = 1 + 7$ (is there any point in "adding" the capacity/ability of the human and that of the vampire in the discussion!?)
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Thank you very much for sharing me your time. I marked @Hans Lundmark's answer as the best one because he pointed me to the historical evidence. And I thank others as well, especially those who pointed out that the dear moderator might have mistaken mere ratio with odds and probability,  

If an amount of money is shared among A and B in the ratio $3:5$ then A gets ${3\over 8}$ of the total, but ${3\over5}$ as much as B.
In my view an expression of the form $a:b$ is NAN (not a number) but a way of talking to be parsed in real time. Mathematically the pair $(a,b)$ can be considered as homogeneous coordinates of a point $p\in{\Bbb P}^1({\Bbb R})$.
