In how many ways can 7 people line up at a ticket window of a cinema hall?
Question:

In how many ways can 7 people line up at a ticket window of a cinema hall?

Solution:

To find: number of arrangements of 7 people in a queue.

Here there are 7 spaces to be occupied by 7 people.

Therefore 7 people can occupy first place.

Similarly, 6 people can occupy second place and so on.

Lastly, there will be a single person to occupy the 7 positions.

Formula:

Number of permutations of $n$ distinct objects among $r$ different places, where repetition is not allowed, is

$P(n, r)=n ! /(n-r) !$

Therefore, permutation of 7 different objects in 7 places is

$P(7,7)=\frac{7 !}{(7-7) !}$

$=\frac{7 !}{0 !}=\frac{5040}{1}=5040$

Therefore, the number of possible ways is 5040