Five books A, B, C, D and E have different thicknesses. A is thicker than C, B is thicker than D, E is thicker than C but not as thick as B, and D is thinner than C. Based on this information, which book is the thinnest among all five?

Introduction / Context:
This question is a classic example of ordering and comparison reasoning. You are given several statements that compare the thickness of different books. From these relational clues, you need to deduce the relative order of all books and then identify the one that is thinnest. Such questions are common in verbal reasoning and help in building skills for handling inequalities and logical ordering problems.

Given Data / Assumptions:

• A is thicker than C.
• B is thicker than D.
• E is thicker than C but not as thick as B.
• D is not as thick as C, so D is thinner than C.
• All five books A, B, C, D and E have different thicknesses.

Concept / Approach:
The approach is to convert all statements into inequalities and then arrange the books in increasing order of thickness. When we say one book is thicker than another, we treat it as a greater than relationship. We combine all given inequalities carefully, making sure there are no contradictions. Once we have a consistent sequence from thinnest to thickest, we can directly read off the thinnest book from the leftmost position in that order.

Step-by-Step Solution:
From “A is thicker than C”, we write A > C. From “B is thicker than D”, we write B > D. From “E is thicker than C but not as thick as B”, we know C < E < B. From “D is not as thick as C”, we know D < C. Now combine these: since D < C and C < E, we have D < C < E. We also know that A is thicker than C, so A > C. We do not yet know if A is thicker than E, but A is definitely thicker than C and D. We already have E < B, so the partial chain becomes D < C < E < B, and A is somewhere to the right of C in this chain. Whatever the exact ordering between A, E and B, it is clear that D is the only one that is thinner than C, and hence thinner than all others.

Verification / Alternative check:
To verify, try placing books in increasing order based on the information. We know D is thinner than C, and C is thinner than E. E is thinner than B. A is thicker than C. A could be between E and B or between C and E, but D remains the only book that is directly stated to be thinner than C, and no other book is stated to be thinner than D. Therefore, D occupies the first position in any valid ordering, making D the thinnest book regardless of the exact positions of A, E and B among the thicker books.

Why Other Options Are Wrong:
A cannot be the thinnest because A is thicker than C, and C is not the thinnest. B cannot be the thinnest because B is thicker than D and also thicker than E. C cannot be the thinnest because D is explicitly thinner than C. E cannot be the thinnest because E is thicker than C and D is thinner than C. Only D satisfies all conditions for being the thinnest.

Common Pitfalls:
One common mistake is to confuse “not as thick as” with “thicker than”, which reverses the inequality. Another error is to try to place all books in a strict complete order prematurely, instead of first identifying clear extremes like the thinnest or thickest. Candidates may also overlook that D is directly compared to C and is stated to be thinner, which is the key clue. Always list all inequalities clearly before drawing conclusions.

Final Answer:
The book that is thinnest among A, B, C, D and E is D.