The word you are looking for is "proportion." A proportion expresses the relationship between two quantities, indicating how one quantity relates to another, often in the form of a fraction or ratio.
"out of"
math fraction in a phrase for t over 12 = t/12
1/2
A number that can't be expressed as a fraction is an irrational number
In that phrase, "unit" means "equal to 1".
out of
"out of"
It is a "rational number".
mathematical phrase
Yes, it is a phrase that indicates time. It will be an adverbial phrase.
math fraction in a phrase for t over 12 = t/12
No, "at first" is not a prepositional phrase. It is an adverbial phrase that indicates the initial stage or the beginning of something.
The same as for "binary tree". Enter that phrase in Answer.com for the definition.
By the enclosure.
since
in any case
repeated phrase or motif