Is Caselets important for CAT DILR?

Candidates can refer to How to Prepare for Logical Reasoning for CAT by Arun Sharma and DI & LR for CAT by Nishit K. Sinha. 

CAT does not have a fixed number of questions from Caselets. Usually, one Caselet-based set with 4-5 questions may appear in the DILR section.

Candidates can refer to High School English Grammar and Composition by Wren and Martin. CAT previous-year questions, grammar exercises and mock tests are also useful.

Yes, understanding Parts of Speech helps candidates improve grammar, sentence correction, para completion and overall Verbal Ability skills.

CAT does not have a fixed number of questions from Parts of Speech. The topic is usually tested indirectly through grammar and Verbal Ability questions.