Sometimes it can be used as Zectico said but you do have to be a bit careful.
you could say that a mixture of 9 parts water and 4 parts vinegar.
The ratio of water to vinegar is 9:4
But altogether there is 13 parts so
the water is $${\frac{{\mathtt{9}}}{{\mathtt{13}}}}$$ of the mixture and
the vinegar is $${\frac{{\mathtt{4}}}{{\mathtt{13}}}}$$ of the mixture
I'm not sure if I understand your question fully, but here's my answer:
9 to 4 or $${\frac{{\mathtt{9}}}{{\mathtt{4}}}}$$
Sometimes it can be used as Zectico said but you do have to be a bit careful.
you could say that a mixture of 9 parts water and 4 parts vinegar.
The ratio of water to vinegar is 9:4
But altogether there is 13 parts so
the water is $${\frac{{\mathtt{9}}}{{\mathtt{13}}}}$$ of the mixture and
the vinegar is $${\frac{{\mathtt{4}}}{{\mathtt{13}}}}$$ of the mixture