We learned that permutation is a arrangement of the elements in an ordered list. When arranging items in specific order we can either use the the permutation formula OR the dash method. The permutation formula can only be used if the question doesn't allow repetition and the dash method will work on basically all situations.
*Remember, You always assume no repetition are allowed otherwise stated*
- Repetition means we are allowed to pick the same item more than once
Restriction are when the questions indicates to place an item in specific location
Examples
-There are 15 horses in a horse show competition. The top three winning horses receive money. How many possible money winning orders are there for a competition with 15 horses?
-Using permutation formula
15P3 = 15! / (15-3)! =2730
or
-Using dash method
15 x 14 x 13 = 2730
-There are 3 brothers and 3 sisters being seated in the bus for a field trip. How many arrangements are possible if they are seated alternately?
*This question uses restrictions therefore we can only use the dash method
3boys x 3girls x 2boys x 2girls x 1boy x 1girl = 36
3girls x 3boys x 2girls x 2boys x 1girl x 1boy = 36
36+36 = 72 ways
Thats pretty much it! If you have any questions or didn't understand something feel free to ask in the comments and I might be able to help you or just google it lol
-Jairo Nato
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