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Question

Seven people, B, C, D, E, F, G, and K, are sitting in a straight line, facing north.
Only two people sit between D and G. Only E sits to the right of K. Only one person sits between G and K. C sits at some place to the right of B but at some place to the left of F.
Who sits third from the right end of the line?

This question was previously asked in
RRB NTPC 2024 Undergraduate CBT 1 Question Paper (29-Aug-2025) (Shift 1)
The correct answer is
F

Solving the Seating Arrangement Puzzle

This puzzle involves arranging seven people (B, C, D, E, F, G, K) in a straight line facing north based on several conditions. The goal is to determine who is seated third from the right end.

Key Constraints Explained

Let's break down the information given:

  • There are 7 people: B, C, D, E, F, G, K.
  • They sit in a straight line facing North. We can represent the positions from left to right as 1, 2, 3, 4, 5, 6, 7.
  • Constraint 1: Only two people sit between D and G. (D _ _ G or G _ _ D)
  • Constraint 2: Only E sits to the right of K. This implies K and E are adjacent, with K immediately to the left of E (KE).
  • Constraint 3: Only one person sits between G and K. (G _ K or K _ G)
  • Constraint 4: C sits to the right of B, and C sits to the left of F. (B ... C ... F)

Step-by-Step Deduction

Combining Constraints on K, E, and G

From Constraint 2, we know the block KE must exist. Now consider Constraint 3 (G _ K or K _ G):

  • Case 1: If G _ K, combined with KE, it forms the block G _ KE. This block uses 4 people.
  • Case 2: If K _ G, combined with KE, it forms the block KE _ G. This block also uses 4 people.

Incorporating Constraint 1 (D and G)

Now let's integrate Constraint 1 (D _ _ G or G _ _ D) with the blocks derived above.

  • Analyzing Case 1 (G _ KE):
    • If D _ _ G: Combining with G _ KE, we need two people between D and G. This suggests an arrangement like D _ _ G _ KE. This sequence uses 7 positions: D, X, Y, G, Z, K, E.
    • If G _ _ D: This doesn't fit easily with the G _ KE block without violating the spacing.
    So, the potential structure derived from Case 1 is D _ _ G _ KE.
  • Analyzing Case 2 (KE _ G):
    • If D _ _ G: Placing this relative to KE _ G could lead to arrangements like D _ KE _ G or D _ _ KE _ G. Checking spacing: D _ KE _ G uses 6 people and implies 3 people (K, E, _) between D and G, contradicting Constraint 1. A structure like D X Y KE Z G uses 7 people and satisfies D _ _ G (DXYG) and K _ G (KEZG). It also satisfies Constraint 2 (KE).
    • If G _ _ D: Combining with KE _ G gives KE _ G _ _ D. This uses 7 positions and satisfies Constraint 1 (G _ _ D), Constraint 2 (KE), and Constraint 3 (K _ G).

Applying Constraint 4 (B, C, F) and Finalizing

Now we place B, C, F according to B ... C ... F into the potential structures.

  • Evaluating Case 1 structure: D _ _ G _ KE The empty slots are positions 2, 3, and 5. The people to place are B, C, F. We need B ... C ... F. The only way to fit B, C, F into the slots (2, 3, 5) respecting the order is: B in 2, C in 3, F in 5. This gives the final arrangement: D B C G F K E. Let's verify all constraints for D B C G F K E: 1. D _ _ G: D B C G (2 people between D and G) - ✓ OK. 2. KE: K E (E is immediately right of K) - ✓ OK. 3. G _ K: G F K (1 person 'F' between G and K) - ✓ OK. 4. B ... C ... F: B C F (C is right of B, C is left of F) - ✓ OK. This arrangement is valid.
  • Evaluating Case 2 structure: KE _ G _ _ D The empty slots are positions 3, 6, and 7. The people to place are B, C, F. We need B ... C ... F. Trying to place them leads to arrangements like K E B G C F D. Checking constraints for K E B G C F D: 1. G _ _ D: G C F D (C, F between G and D) - ✓ OK. 2. KE: K E - ✓ OK. 3. K _ G: K E B G (E, B between K and G) - X Fails! Constraint 3 says *only one* person between K and G. This arrangement has two. Therefore, this structure derived from Case 2 is invalid.
  • Evaluating Case 2 structure: D X Y KE Z G The empty slots are X, Y, Z. People B, C, F need to be placed. We need B ... C ... F. A possible placement is D B C KE F G. Checking constraints for D B C KE F G: 1. D _ _ G: D B C G (B, C between D and G) - ✓ OK. 2. KE: K E - ✓ OK. 3. K _ G: K E F G (E, F between K and G) - X Fails! Constraint 3 requires only one person between K and G. This structure is also invalid.

Final Arrangement and Answer

The only valid arrangement satisfying all conditions is:

Position (Left to Right) 1 2 3 4 5 6 7
People D B C G F K E

Now, let's find the person third from the right end:

  • The person at the right end (7th position) is E.
  • The person second from the right end (6th position) is K.
  • The person third from the right end (5th position) is F.

Therefore, F sits third from the right end of the line.

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Similar Questions

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  2. A, B, E, F, L, M and P are sitting around a circular table, facing the centre. Only three people sit between P and E when counted from the left of P. Only three people sit between M and A when counted from the right of A. L sits to the immediate right of M. F is an immediate neighbour of A as well as E. Who sits second to the left of B?

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Important Questions from Seating arrangement

  1. Five people A, B, C, D and E are seated about a round table. Every chair is spaced equidistant from adjacent chairs. 

    (i) C is seated next to A 

    (ii) A is seated two seats from D 

    (iii) B is not seated next to A 

    On the basis of above information, which of the following must be true? 

    1. D is seated next to B 

    2. E is seated next to A 

    3. D and C are separated by two seats 

    Select the correct answer using the code given below:

  2. There are seven persons up on a ladder, A, B, C, D, E, F and G (not in that order). A is further up than E but is lower than C. B is in the middle. G is between A and B. E is between B and F. If F is between E and D, the person on the bottom step of the ladder will be

  3. Consider that: 

    1. A is taller than B. 

    2. C is taller than A. 

    3. D is taller than C. 

    4. E is the tallest of all. 

    If they are made to sit in the above order of their height, who will occupy the mid position?

  4. Four children are sitting in a row. A is occupying the seat next to B but not next to C. If C is not sitting next to D, who is/are occupying seat/seats adjacent to D?

  5. A question paper must have a question on one of the eight poets: A, B, C, D, E, F, G or H The first four belong to the medieval period while the rest are considered modern poets Generally, modern poets figure in the question paper in alternate years. Generally those who like H like G also; and those who like F like E also. The paper-setter does not like to ask about F as he has written a book on F, but he likes F. Last year, the paper contained a question on A. 

    On the basis of the information given, this year's paper is most likely to contain a question on

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