Difference between quiz question and lesson examples

Question

« Je possède trois appartements, ---- deux sont loués » is one of the kwiziq questions in this section.

« J'ai trois enfants, dont deux qui sont au collège. » is one of the examples from the lesson.

Also from the lesson " If including / [number] of which is followed by a conjugated verb, in French you need to add a relative pronoun (qui or que / qu') in front of the verb. "

There is no space in the question to write "dont deux qui sont loués" in the quiz answer.

Is this a mistake in the question/answer format, or is there a grammatical reason for the difference -eg passive voice - that I am missing ? The explanation and examples in the lesson do not seem to match the answer this question, as presented, appears to call for.

Accepted Answer

Bonjour Maarten,
Thank you for pointing this out! 'Qui' has now been added to the sentence.
Merci de votre contribution et bonne journée !

Answer

It's curious though, if you do a google search for the phrases "dont deux [qui] sont loués", it seems that "qui" is usually omitted.

"dont deux qui sont loués" - 3 hits, including 1 on kwiziq

"dont deux sont loués" - 81 hits.

I couldn't find this rule in Le Bon Usage. There is a section on "dont" complemented by a number, but it gives the example: "Vous m'avez prêté des romans dont trois m'ont intéressé".