Question about the sentence: "El kilo de tomates cuesta seis pesos."
From Rosetta Stone:
The customer asks how much the tomatoes are. The farmer replies:
"El kilo de tomates cuesta seis pesos."
I´m wondering if that is a typical response to such a query and why he didn´t just say "Un kilo de tomates cuesta seis pesos."?
P.S. Just to make sure I´m starting from the right perspective, my translation of his sentence is "The tomatoes are six pesos a kilo"
5 Answers
El kilo de tomates cuesta 6 pesos is quite usual. The use of el kilo is like tomatoes by the kilo cost 6 pesos HERE. There is nothing wrong with Un kilo de tomates cuesta 6 pesos. But that would be a more loose statement. It could be a general statement being made about the price of tomatoes.
"Los dejo en seis por kilo" "Valen seis por kilo." "Valen ocho, pero los vendo en seis por tí. Ya es tarde, sabes."
Either un or el could have been used.
I think you will find, in general, that Spanish uses the definite article a bit more often than English, including both places where we´d use the indefinite or a personal pronoun (the latter especially in reflexive constructions) and in places we might not necessarily use an article at all. It´s just something you have to get used to, and soon will.
Spanish often uses a definite article for very general things. Me gusta la música, vs I like music (an example of where we don´t bother with an article). So, your example is just saying that kilos of tomatoes cost 6 pesos (in general)
Basically, don´t overthink it. It´s normal to notice it (I certainly do anyway) but best to just make note of it and go on. It´s just a little different. You´re going to run into that, a LoT! 
The kilo of tomatoes cost six pesos.
One kilo of tomatoes cost six pesos, is the other you wrote.
And Los tomates están seis pesos por kilo. What you wrote in English.
I agree with donbigote
