391. Five books—A, B, C, D, E—are placed in a row. A is not next to B, and C must be at one of the ends. If D is immediately to the left of E but not next to A, what is the possible order of books from left to right?
Key Concept: Logical Arrangement, Constraints
b) A, D, E, B, C
[Solution Description]
To solve this arrangement:
1. Since C is at one end, it can be first or last.
2. D is immediately left of E (D-E pair) and not next to A.
3. A is not next to B.
Testing C as first: Possible orders: C, D, E, A, B → invalid (A-B adjacent). Another option: C, A, D, E, B → valid.
Testing C as last: Possible orders: A, D, E, B, C → valid.
Hence, two orders work: C, A, D, E, B and A, D, E, B, C.
Only A, D, E, B, C is among the options.
Your Answer is correct.
b) A, D, E, B, C
[Solution Description]
To solve this arrangement:
1. Since C is at one end, it can be first or last.
2. D is immediately left of E (D-E pair) and not next to A.
3. A is not next to B.
Testing C as first: Possible orders: C, D, E, A, B → invalid (A-B adjacent). Another option: C, A, D, E, B → valid.
Testing C as last: Possible orders: A, D, E, B, C → valid.
Hence, two orders work: C, A, D, E, B and A, D, E, B, C.
Only A, D, E, B, C is among the options.
