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Question

Six people are seated around a circular table. There are at least two men and two women. There are at least three right-handed persons. Every woman has a left-handed person to her immediate right. None of the women are right-handed. The number of women at the table is

The correct answer is

2

Analyzing the Circular Table Seating Puzzle

This problem requires us to determine the number of women seated at a circular table based on several conditions related to gender and handedness. Let's break down the information given:

  • There are 6 people in total.
  • The arrangement is a circular table.
  • There are at least 2 men and at least 2 women. Let $N_W$ be the number of women and $N_M$ be the number of men. So, $N_W + N_M = 6$, with $N_W \ge 2$ and $N_M \ge 2$. This limits the possibilities for the number of women to 2, 3, or 4.
  • There are at least 3 right-handed persons. Let $N_R$ be the number of right-handed people and $N_L$ be the number of left-handed people. Then $N_R + N_L = 6$. The condition $N_R \ge 3$ implies that $N_L = 6 - N_R \le 6 - 3 = 3$. Therefore, $N_L \le 3$.
  • Every woman has a left-handed person to her immediate right.
  • None of the women are right-handed. This means all women are left-handed ($W \implies L$).

Deriving Key Constraints

From the conditions, we can establish crucial relationships:

  • Since all women are left-handed ($W \implies L$), the total number of left-handed people ($N_L$) must be at least the number of women ($N_W$). So, $N_L \ge N_W$.
  • Combining this with the earlier deduction ($N_L \le 3$), we get the combined constraint: $N_W \le N_L \le 3$.

Evaluating Possible Scenarios for Number of Women

We will now test the possible values for $N_W$ (which are 2, 3, or 4) against the derived constraint $N_W \le N_L \le 3$ and the condition that every woman has a left-handed person to her right.

Scenario 1: Assuming 4 Women ($N_W=4$)

If there are 4 women ($N_W=4$), the constraint $N_W \le N_L \le 3$ becomes $4 \le N_L \le 3$. This is impossible, as the number of left-handed people cannot be both greater than or equal to 4 and less than or equal to 3.

Therefore, $N_W=4$ is not possible.

Scenario 2: Assuming 3 Women ($N_W=3$)

If there are 3 women ($N_W=3$), the constraint $N_W \le N_L \le 3$ becomes $3 \le N_L \le 3$. This means we must have exactly $N_L=3$ and $N_R=3$. Since all women are left-handed ($W \implies L$), the 3 women must be the only left-handed people ($W_1(L), W_2(L), W_3(L)$). Consequently, the remaining 3 people must be men ($N_M=3$), and they must all be right-handed ($M_1(R), M_2(R), M_3(R)$).

Now let's check the condition: "Every woman has a left-handed person to her immediate right."

Consider any arrangement. Let the seats be numbered 1 to 6. If women are placed non-contiguously, e.g., W at 1, 3, 5. Then people at seats 2, 4, 6 must be L. But only the women are L, so seats 2, 4, 6 would have to be occupied by women, which contradicts $N_W=3$.

If women are placed contiguously, e.g., W at 1, 2, 3. Then $W_1(L)$ at 1, $W_2(L)$ at 2, $W_3(L)$ at 3. The person to the right of $W_1$ is $W_2$, who is L (satisfies condition). The person to the right of $W_2$ is $W_3$, who is L (satisfies condition). The person to the right of $W_3$ (at seat 4) must be L. However, seat 4 must be occupied by a man, and we deduced all men must be right-handed. This creates a contradiction.

Therefore, $N_W=3$ is not possible.

Scenario 3: Assuming 2 Women ($N_W=2$)

If there are 2 women ($N_W=2$), the constraint $N_W \le N_L \le 3$ becomes $2 \le N_L \le 3$. This means $N_L$ can be 2 or 3. If $N_W=2$, then $N_M=4$. Let's check the condition "Every woman has a left-handed person to her immediate right."

Consider the case where the two women sit together: $W_1, W_2$. Let $W_1$ be at seat 1 and $W_2$ at seat 2.

  • $W_1$ is Left-handed ($W_1(L)$).
  • $W_2$ is Left-handed ($W_2(L)$).
  • The person to the right of $W_1$ is $W_2$, who is L. This condition is met.
  • The person to the right of $W_2$ (at seat 3) must be L. Since there are only 2 women, this person must be a man. Let's call him $M_1$. So, $M_1$ must be Left-handed ($M_1(L)$).
  • Now we have identified 3 left-handed people: $W_1(L), W_2(L), M_1(L)$. This means $N_L \ge 3$.
  • Combined with the constraint $N_L \le 3$, we must have exactly $N_L=3$.
  • If $N_L=3$, then $N_R = 6 - 3 = 3$.
  • The remaining 4 men ($N_M=4$) must fill the other seats. We have already identified $M_1$ as L. The remaining 3 men must be right-handed ($M_2(R), M_3(R), M_4(R)$).
  • A possible arrangement satisfying these conditions is: $W_1(L), W_2(L), M_1(L), M_2(R), M_3(R), M_4(R)$ around the table.
  • Let's verify all original conditions for this arrangement:
    • 6 people total: Yes.
    • Gender: 2 Women, 4 Men (satisfies $N_W \ge 2, N_M \ge 2$).
    • Handedness: 3 Left, 3 Right (satisfies $N_R \ge 3$).
    • Women handedness: $W_1, W_2$ are L (satisfies $W \implies L$).
    • Neighbors: $W_1$'s right neighbor is $W_2$(L). $W_2$'s right neighbor is $M_1$(L). (satisfies condition).

This scenario works perfectly.

Conclusion

The only scenario that satisfies all the given conditions is when there are 2 women.

The number of women at the table is 2.

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Important Questions from Numerical Reasoning

  1. A traveller to the town reaches a crossroad. Upon asking residents A, B and C for directions to a certain destination, he gets the following responses

    A: turn left

    B: do not turn left

    C: go straight

    If only one among A, B and C is truthful, the traveller 

  2. In a city, each person has at least one hair on his/her head. At least two persons in this city are guaranteed to have exactly the same number of hair on their heads if the population of the city

  3. a, b, c are real numbers. The quadratic equation ax2 – bx + c = 0 has equal roots, which is β, then

  4. S, M, E and F are working in shifts in a team to finish a project. M works with twice the efficiency of others but for half as many days as E worked. S and M have 6 hour shifts in a day, whereas E and F have 12 hours shifts. What is the ratio of contribution of M to contribution of E in the project?

  5. If x>y>1, which of the following must be true?

    (i) In x > In y

    (ii) ex > ey

    (iii) y2 > x2

    (iv) cos x > cos y
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