の can be used in place of a noun (pronoun) to mean 'one' or 'some'
Construction: Use in place of noun
青いの。 aoi no. The blue one. 安いのがほしい。 yasui no ga hoshii. I want the cheap one. (computer, car, book, anything)
青いの。 aoi no. The blue one.
安いのがほしい。 yasui no ga hoshii. I want the cheap one. (computer, car, book, anything)