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In a doctor's waiting room, there are 14 seats in a row. Eight people are waiting to be seated. Three of the 8 are in one family, and want to sit together. How many ways can this happen?

Respuesta :

There are 14 chairs and  8 people to be seated. But among the 8. three will be seated together:

So 5 people and (3) could be considered as 6 entities:

Since the order matters, we have to use permutation:

¹⁴P₆ = (14!)/(14-6)! = 2,162,160, But the family composed of 3 people can permute among them in 3! ways or 6 ways. So the total number of permutation will be ¹⁴P₆  x 3! 

2,162,160 x 6 = 12,972,960 ways.

Another way to solve this problem is as follow:

5 + (3) people are considered (for the time being) as 6 entities:

The 1st has a choice among 14 ways
The 2nd has a choice among 13 ways
The 3rd has a choice among 12 ways
The 4th has a choice among 11 ways
The 5th has a choice among 10 ways
The 6th has a choice among 9ways

So far there are 14x13x12x11x10x9 = 2,162,160 ways
But the 3 (that formed one group) could seat among themselves in 3!
or 6 ways:

Total number of permutation = 2,162,160 x 6 = 12,972,960

Since 3 members want to sit together, we'll calculate total ways for it and then for remaining seats in each of its case, we'll see in how many ways can those rest of 5 people wants to sit.

The total number of ways those 8 people can sit is 3,991,680 ways.

Given that:

  • Total 14 seats are there in a row in a doctor's waiting room.
  • 8 people are waiting to be seated.
  • 3 people are of same family and want to sit together.

To find:

In how many ways can those people sit?

Number of ways in which 3 family members can sit:

Since 3 people wants to sit together, then suppose seats are numbered 1,2,3,...,14.

Then those 3 people can choose seats as:

1,2,3

2,3,4

...

...

12,13,14

Total 12 ways.

In each way, those three can sit on those 3 chairs in any order. The number of ways 3 people will arrange themselves is 3! = 6 ways.

Thus:

Total ways those 3 people can sit in = 12 times 6 = 72 ways.

( i did multiplication since for each of 3 seat chosen they were sitting in 6 ways, and this repeated 12 times would end up on 12 times 6 = 72 ways).

Number of ways those remaining 5 people can sit on remaining 11 seats:

On remaining seats (14-3 = 11), we have 5 people to sit.

Those people can choose any seat they want to sit on.

Total ways(combinations) they together choose 5 seats is given by: [tex]^11C_5 = 462 [/tex]

For each of those choice of seats, they can arrange themselves in 5! = 120 ways.

Thus, those 5 people can sit in 120 times 464 = 55440 ways.

Since on each choice of those 3 family members , we have 55440 ways of 5 people sitting on remaining 11 seats, thus in total we have:

55440 times 72 = 3,991,680 ways.

Thus, in total, those 8 people can sit in 3,991,680 number of ways in that row of the doctor's waiting room.

Learn more about combinations here:

https://brainly.com/question/10618762