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Question

Six persons A, B, C, D, E and F are sitting in a row facing towards north (not necessarily in the same order). Their ages are in successive multiple of 3 from left to right end. B is second to the right of A. A is to the immediate left of E. Only three persons sit between C and F. The age of D is 18 years and the maximum. C sits to the left of E. What is the total age of A and B?

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
18 years

Logic Puzzle: Seating Arrangement and Ages

This problem requires determining the seating positions and ages of six individuals based on given clues to find the sum of ages for A and B.

1. Assigning Ages Based on Clues

The ages are successive multiples of 3. Given that D has the maximum age of 18 years, the ages from left to right must be:

  • Position 1: $3$
  • Position 2: $6$
  • Position 3: $9$
  • Position 4: $12$
  • Position 5: $15$
  • Position 6: $18$

Since D has the maximum age (18 years), D is located at the rightmost position ($P_6$).

2. Determining Relative Positions

Analyze the positional clues:

  • 'A is immediate left of E' implies the arrangement $AE$.
  • 'B is second to the right of A' means B is at position $A+2$. Combined with $AE$, this forms a block $AEB$.
  • 'C sits to the left of E' implies $C$ is somewhere before $E$.
  • 'Only three persons sit between C and F'.

3. Deriving the Final Arrangement

Consider the possible placements for the $AEB$ block:

  • Attempt 1: $A E B$ in positions $P_1, P_2, P_3$. The row starts $A \ E \ B \ \_ \ \_ \ D$.
    • Ages: $A=3, E=6, B=9, D=18$.
    • The clue '$C$ sits to the left of $E$' cannot be satisfied as $P_1$ (left of $E$ at $P_2$) is occupied by $A$. This case fails.
  • Attempt 2: $A E B$ in positions $P_2, P_3, P_4$. The row is $\_ \ A \ E \ B \ \_ \ D$.
    • Ages: $D=18$ (at $P_6$). The remaining positions $P_1$ and $P_5$ are for $C$ and $F$.
    • $E$ is at $P_3$. '$C$ sits to the left of $E$' implies $C$ must be at $P_1$.
    • The arrangement becomes $C \ A \ E \ B \ P_5 \ D$. $P_5$ must be $F$.
    • Row: $C \ A \ E \ B \ F \ D$.
    • Check '3 persons between C and F': $C$ is at $P_1$, $F$ is at $P_5$. The persons $A, E, B$ (at $P_2, P_3, P_4$) are between them. This condition is met. This is the correct arrangement.
  • Attempt 3: $A E B$ in positions $P_3, P_4, P_5$. The row is $\_ \ \_ \ A \ E \ B \ D$.
    • Ages: $A=9, E=12, B=15, D=18$.
    • $P_1$ and $P_2$ are for $C$ and $F$. The maximum number of persons between $C$ and $F$ is 1 (if they are at $P_1, P_2$). This violates the condition of 3 persons between them. This case fails.

The confirmed arrangement is $C \ A \ E \ B \ F \ D$ with ages $3, 6, 9, 12, 15, 18$ respectively.

4. Calculating the Total Age of A and B

In the confirmed arrangement:

  • A is at Position 2, Age(A) = $6$ years.
  • B is at Position 4, Age(B) = $12$ years.

The total age of A and B is Age(A) + Age(B) = $6 + 12 = 18$ years.

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  3. Five students are standing in a line. Suman is standing next to Pranav but not next to Deena. Kumar is standing next to Raju, who is standing on the extreme left, and Deena is not standing next to Kumar.

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