Which of the following statements is not correct with regard to a mathematics…

Sound design of a mathematics textbook rests on a few accepted principles: examples should connect to the daily life of students so the content feels meaningful, the book should stay reasonably light and manageable, and it must combine worked (solved) examples that model reasoning with ample unsolved practice exercises — since students build genuine problem-solving skill only by attempting problems on their own.

Judged against this principle, the claim that a mathematics textbook should carry "solved examples only" fails: it removes every opportunity for independent practice, so it is the statement that is not correct about good textbook design.

Checking each statement against the same principle:

• Linking examples to students' daily life aids comprehension and motivation — a valid guideline, so this statement stands.

• Avoiding an overly thick or heavy book keeps it manageable for young learners — a valid guideline, so this statement stands.

• Offering varied exercises gives students the practice they need to build skill — a valid guideline, so this statement stands, and it is exactly the requirement that "solved examples only" would violate.

Hence, the statement that a mathematics textbook should have solved examples only is the one that is not correct.