How many Spaniards speak Castilian Spanish 15 of the population 27 53 74 population?

You're asking about the percentage of the Spanish population that speaks Castilian Spanish. Here's how to figure that out:

* Castilian Spanish is the official language of Spain.

* Virtually all Spaniards speak Castilian Spanish.

Therefore, a very high percentage of Spaniards speak Castilian Spanish, likely over 99%. It's not possible to give an exact number without a very specific survey.