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Question

If 3 men and 2 women are seated in a row, how many seating arrangements are possible such that no woman is seated next to
another woman?

The correct answer is
36

Solving Seating Arrangement Constraints

This problem involves finding the number of possible ways to arrange 3 men and 2 women in a single row, with a specific condition: no two women should be seated next to each other.

Arranging the Men

The first step is to arrange the individuals who do not have adjacency restrictions, which are the 3 men. Assuming the men are distinct individuals (e.g., M1, M2, M3), the number of ways to arrange them in a row is calculated using permutations.

  • The number of permutations for $n$ distinct items is $n!$.
  • For 3 men, the number of arrangements is $3!$.
  • Calculation: $3! = 3 \times 2 \times 1 = 6$.

So, there are 6 distinct ways to arrange the 3 men.

Identifying Woman Positions

After seating the men, we need to determine the possible positions where the women can be seated so they are not adjacent to each other. Consider the arrangement of the 3 men (represented by 'M'). This creates potential spaces (represented by '_') for the women:

$_ M _ M _ M _$

  • There are 4 possible spaces where the 2 women can be seated. Placing women in any two of these distinct spaces guarantees that they will not be sitting next to each other, as each space is separated by at least one man.

Placing the Women

Now, we need to place the 2 women into the 4 identified spaces. To ensure they are not together, we must select 2 distinct spaces out of the 4 available. The number of ways to choose $k$ items from a set of $n$ items without regard to the order of selection is given by the combination formula $C(n, k) = \frac{n!}{k!(n-k)!}$.

  • Here, we need to choose 2 spaces ($k=2$) from the 4 available spaces ($n=4$).
  • Calculation: $C(4, 2) = \frac{4!}{2!(4-2)!} = \frac{4!}{2!2!} = \frac{4 \times 3 \times 2 \times 1}{(2 \times 1)(2 \times 1)} = \frac{24}{4} = 6$.

There are 6 ways to choose the pair of spaces where the women will sit.

Calculating Total Arrangements

The total number of possible seating arrangements where no two women sit together is found by multiplying the number of ways to arrange the men by the number of ways to choose the spaces for the women.

  • Total Arrangements = (Number of ways to arrange men) $\times$ (Number of ways to choose spaces for women)
  • Total Arrangements = $3! \times C(4, 2)$
  • Total Arrangements = $6 \times 6 = 36$.

This calculation method yields 36 possible seating arrangements under the given condition.

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Important Questions from Permutation and Combination

  1. m parallel lines cut n parallel lines giving rise to 60 parallelograms. What is the value of (m + n) ?

  2. 5-digit numbers are formed using the digits 0, 1, 2, 4, 5 without repetition. What is the percentage of numbers which are greater than 50,000 ?

  3. In a race, there are 4 members in a team. Each member has to cover 5 km one after another. If the total time taken is 30 minutes, then what would have been the average speed?

  4. If Quantity A is the number of ways to assign a number from 1 to 5 without repetition to each of four people, and Quantity B is the number of ways to assign a number from 1 to 5 without repetition to each of 5 people, then which of the following statements is correct with respect to Quantities A and B?

  5. Which of the following muscles regulates the exit of food from the stomach into the small intestine?

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