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Question

There is a group of 5 people among which there is one couple. In how many ways can these 5 people be seated in a row having 5 chairs if the couple is to be seated next to each other?

The correct answer is
120

Seating Arrangement Logic

The problem asks for the number of ways to seat 5 people in a row such that a specific couple always sits together.

Treating the Couple as a Unit

To ensure the couple sits together, we can treat them as a single conceptual unit. Let the 5 people be P1, P2, P3, P4, P5, and let P1 and P2 be the couple.

  • Consider the couple {P1, P2} as one block, let's call it 'C'.
  • Now, we need to arrange the block 'C' and the remaining 3 people (P3, P4, P5).
  • This gives us 4 entities to arrange: {C, P3, P4, P5}.

Calculating Arrangements

The number of ways to arrange these 4 distinct entities in a row is given by the factorial of 4:

$ 4! = 4 \times 3 \times 2 \times 1 = 24 $

Within the couple's block 'C', the two people (P1 and P2) can switch places. They can be seated as (P1, P2) or (P2, P1).

The number of ways the couple can arrange themselves is:

$ 2! = 2 \times 1 = 2 $

Total Number of Ways

To find the total number of ways to seat the 5 people with the couple together, we multiply the number of ways to arrange the entities by the number of ways the couple can arrange themselves internally:

$ \text{Total Ways} = (\text{Ways to arrange 4 entities}) \times (\text{Ways to arrange couple internally}) $

$ \text{Total Ways} = 4! \times 2! = 24 \times 2 = 48 $

Therefore, there are 48 distinct ways to seat the 5 people such that the couple sits next to each other.

Option Analysis

The calculated answer is 48, which corresponds to Option B.

Option 1: 24
Option 2: 48
Option 3: 60
Option 4: 120
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Important Questions from Quick Math

  1. Evaluate $5.29 \bar{8} - 6.29 \bar{8} + 7.29 \bar{8} $

  2. If + means -, - means $\times$, $\times$ means $\div$  and $\div$ means +, then what will come in place of the question mark (?) in the following equation?
    $29+14\times7\div11-9=?$

  3. The average age of father and elder son is 35 years, the average age of father and younger son is 32 years and the average age of the two sons is 17 years. What is the average age of the father and his two sons?
  4. A car travels $\frac{1}{4}$th of the distance at a speed of 60 km/hr and the remaining $\frac{3}{4}$th of the distance at a speed of $v$ km/hr. If the average speed for the full journey is 50 km/hr, then the value of $v$ is

  5. If the average of the first four of five numbers in decreasing order is 25 and the average of the last four numbers is 20, then what is the difference between the first and the last number?
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