How would you use permutations to find the arrangements possible

Roland Manning

Roland Manning

Answered question

2022-06-25

How would you use permutations to find the arrangements possible if a line has all the boys stand together?

Answer & Explanation

massetereqe

massetereqe

Beginner2022-06-26Added 21 answers

Step 1
If the boys are inserted together in a line of G girls, there are ( G + 1 ) different places the boys could be inserted each giving a different arrangement.
(One way to see this is to consider how many girls would be to the left of the group of boys; the choices are { 0 , 1 , 2 , ... , G } for ( G + 1 ) different possibilities.
The girls could be arranged in G! different sequences:
G choices for the first position;
XX ( G - 1 ) for the second (once the first has been determined)
XXXX ( G - 2 ) for the third (once the first two have been determined)
XXXXXX ( G - 3 ) for the fourth...
and so on, until ...
2 for the second last position
1 for the last position.
Step 2
For a combination of XXX G × ( G - 1 ) × ( G - 2 ) × ( G - 3 ) × ... × 2 × 1 = G ! different permutations.
Similarly the boys could be arranged in B! different permutations.
So for each of the ( G + 1 ) locations where the boys could be inserted in the line of girls
there are G! permutations of girsl, and for each of these joint combinations there are B! permutations of boys.
Giving ( G + 1 ) G ! B ! different permuations.

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