# "130 yen to the dollar" VS "130 yen to a dollar"

I saw this sentence in the dictionary on my phone(so I can't get a link to it here):

We're only getting 130 yen to the dollar at the moment.

I'm wondering why the definite article 'the' is being used instead of indefinite article 'a'? Can we instead say: We're only getting 130 yen to a dollar at the moment?

I've also seen other examples in which 'the' is used instead of 'a':

The car will do over 40 miles to the gallon.

The scale of your map is one inch to the mile.

However, I did see an example in which 'a' is used instead of 'the':

There are just over four and a half litres to a gallon.

Can someone help to explain why sometimes 'a' is used and sometimes 'the' is used? Or they are just interchangeable in those scenarios?

• "a dollar" is a more general term for 1USD, But here the dollar could be 1CAD or 1AUD. Even here i used "the dollar" in my comment because i know which dollar i am talking about. You can search about "definite and indefinite article in sentences"
– 0_o
Commented Oct 17, 2018 at 9:18

## 2 Answers

I don't think they're interchangeable --- as a native speaker (western US) I would only use:

We're only getting 130 yen to the dollar. (not 'to a dollar')
There are just over four and a half liters to a gallon. (not 'to the gallon')

I'm less sure about the middle examples. Probably I would say both of them with 'per':

The car will do over 40 miles per gallon.
The scale of your map is one inch per mile.

Sorry I can't come up with a good reason for these different usage patterns. I'm not sure there is a good reason. I just think of "{currency} to the {currency}" as a standard phrase.

Regarding your first example, I believe the use of the definite article is correct as it involves the specific value of "the dollar" as currency at that specific time. Thank you