Learn Finnish: Tuotteet, joiden kysyntä on suurta, ovat kalliita. - The products whose demand is high are expensive.

The noun it describes, kysyntä (demand), is an abstract, uncountable concept. In Finnish, when an adjective describes an uncountable subject, the describing word (the predicative adjective) must be in the partitive case.

How do we get "whose" from the word joiden?

Joiden is the genitive plural form of the relative pronoun joka (which/who). Because it points back to the plural noun tuotteet (products) and is in the genitive (possessive) case, it translates directly to "of which" or "whose".

Why is kalliita in the partitive plural instead of the nominative plural?

In a general sentence with a plural subject like tuotteet, the describing adjective is put in the partitive plural. You would only use the nominative plural kalliit if you were talking about a specific, closed group of items as a total whole, rather than making a general descriptive statement about products.

Is kysyntä related to the verb kysyä?

Yes! Kysyntä (demand) is derived from the verb kysyä (to ask). The suffix -ntä or -nta is often used to turn verbs into nouns that describe the action or phenomenon of the verb, so the concept of "asking" becomes "demand" in an economic sense.