Veintiun or veintiuno?

Question

If I say "They cost twenty-one dollars," would it be "Cuestan veintiun dolares" or "Cuestan veintiuno dolares"? How can I tell when to use each one?

Answer 1

"Cuestan Vientiun dolares" is right one. You can answer Ventiuno when they ask you, for example, your age, how many days to this or that and it applies to other things too but I can't put my finger on them right now.

Answer 2

the 'cuestan veintiun dolares is the most used, and the proper one however since your asking for the proper manner to write
or pronounce this specific application of the word in your question
and taking in consideration the word 'They' (giving the plural meaning of it),the 'cuestan veintiun dolares' is the correct linguistically manner to address your query,
now,here are other possibilities to build some better skills in terms of saying the same answer but in a more formal approach ;
1)El costo de los mismos es de veintiun dolares.
2)tienen un costo total de veintiun dolares
3)veintiun dolares es el precio de estos.
'veintiuno' refers as a whole but in a singular unit term;descriptive and in the future tense of the number;,
examples will be as;
today's date ,quantities of specific items ,measurements standards,just to name a few,to provide you with a brief ,
but meaningful application of the subject in question.

Answer 3

Cuestan veintiún dólares
when 21 is acting as a determinant use veintiún, and when its is only a number acting as a noun then use veintiuno

Answer 4

either or is ok to use but i like veintiuno better :)