A question about the study question 「僕の母はいつも分の厚い本を読んでいます。」

[Sirh]

Should be 分厚い instead of 分の厚い right? Or I’m missing something

[cafelatte]

both are valid!

A question about the 練習問題 「僕の母はいつも____の厚い本を読んでいます。」

Is this construction of 分の厚い real? I’ve tried googling it and I’m not getting any hits. Instead all I see is 分厚い, which also exists as a word on bunpro.