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Possible Duplicate:
Do values attached to integers have implicit parentheses?
What is 48÷2(9+3)?
What is “multiplication by juxtaposition”?

What is the precedence of the concatention operator when used for multiplication?

If it's the same as multiplication, 5/7y would mean (5/7)*y.

However, it also seems reasonable to see it as 5/(7*y).

I realize I can avoid the issue by writing "5y/7" or using explicit parentheses, but am curious about the "correct" answer.

Googling was surprisingly unhelpful: most results were about the precedence of string concatention in programming languages.

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    No need to out quotes in the title, makes it harder to read.2012-08-26

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I think that you almost answered your own question:

I realize I can avoid the issue by writing "5y/7" or using explicit parentheses.

I don't know of any "correct" way to interpret $5/7y$, and I don't believe that there is any. There are lots of notations in math that are not that clear, and the only answer is to make them clear. So I would never write $5/7y$ on a blackboard if I meant $5/(7y)$.

If you by $5/7y$ mean $5/7*y$, then from what I understand, when programming a compiler would interpret this as $5*y/7$.

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    Speaking of Mathematica, IIRC [Singular](http://www.singular.uni-kl.de/) also interprets juxtaposition as multiplication.2012-08-26
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I believe concatenation strictly applies to the joining of two strings together. I would imagine that extending this to mathematical operations there would be parenthesis around the objects in order to avoid ambiguity, ie $ 5/7 * y/x $ would yield $\dfrac{5}{7}\cdot\dfrac{y}{x}$