Hey guys its Darian, I know its been a while but I finally did it :P.
Today we learned about Circular Permutations and as you can guess by the name, They involve Circles, Thats it thats the blog, circles are awesome.
Just kidding, now really a circular permutation does not have a first or last. The position in the circle are relative to the other objects of this circle. Therefore, all of the permutations that we deal with will be placed around the placement of the first thing placed. (Too many placements).
The number of permutations of n objects in a circle is (n-1)! you minus one because someone always has to be seated first so the following arrangements of people around a circle are more so based apon the people who are not seated first and the places they will sit.
Ex.1 We have a table that can sit 12 people and in turn there are 12 people who are going to sit down, they can sit wherever they feel like, How many ways can these 12 people sit.
Now a question like this is probably one of the easiest questions we will have, all you do is use the formula.
number of permutations=(n-1)!
number of permutations=(12-1)!=11!
number of permutations= 39,916,800
Now circular permutations are not always so simple, We can have restrictions on our circular permutations questions such as, two people have to sit together, two people must not sit together,the people at the table must alternate,etc.
Ex.2 How many ways can 4 friends (Tony,Steve,Bruce,Thor) be seated together around a circular table, if Jackie refuses to sit near any of them and there are 4 people already at the table and the table sits 12.
Well first you would draw a diagram
Then we would use the equation nPr to calculate the total amount of placements for Jackie
nPr n=5 r=1
5P1= 5
Now to calculate the the amount of permutations for the 4 other people and because there is 6 places left to sit and they can sit in any of them, calculating the amount of permutations is easy all you do is use the dashed method.
And now you count the 4 friends as 4! and put and equation together to find the total number of permutations
Which would be : 4!x5x360= 43 200
You may have questions in which you have to make multiple dashed line methods and add them together this is one of them.
Ex.3
How many 8 digit numbers greater than 56,000,000 can be formed using the numbers 4,4,4,5,5,6,7,and 8
To solve this equation you must make 2 dashed line methods and add their answers.
and
you then add the two numbers you get from these methods which are 360 and 1260 and add them to get your final answer which is 1620.
And finally a common exam question is a question about keys and how many different permutations can be made with the keys, this may seem straight forward but there is a trick because the keys are double sides and they are the same on both sides you must divide the answer you get using the circular permutations equation by 2!.
Ex.4
How many different key rings can be made of 12 different color coded keys.
You start out using the Circular Permutations equation which is pretty straight forward
(n-1)=?!
(12-1)=11!
11!=39,916,800
Now Divide this answer by 2! and you get your final answer
39,916,800 ÷ 2! = 19,958,400
Thats it, Thanks for reading, I hope you enjoyed this scribe and learned something from it, If you didnt follow everything I scribed, uhmmmm Ask Mr.P he can probably tell you :P.
Thanks for reading and now heres a squirrel.