exams up next week and i still cant get permutation and combination on s1 as level. plzzz help!!!

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i couldnt understand the concept itself.. its getting on my nerves. although i have tries several times .. yet i havent understood the main concept and where d formulas are supposed to be applied. jus this paper is gonna SPOIL my entire exam!!! PLZZZ HELP ME OUT ... :(

Posted Fri 2nd March, 2012 @ 06:06 by Alisha prasai

1 Answer

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When the order matters we are looking at permutations and if the order is irrelavent then we are looking at combinations.

With both of these you can split up into examples when we use repetitions for example if i was to have a code for a bike lock i can use 0-9 for each number but they could be repeated. Or examples without repetitions as when we choose lottery numbers as numbers can only appear once.

This is why we have a range of formulas. To begin these questions you need to decide does the order of events matter ( Permutation or Combination) Once you are sure of this you need to decide if the numbers can be repeated or not. This will help you decide which formula to use.

Permutations with repetition                  Formula = nr       (Repetition allowed, order matters)

Permutations without  repetition                      (http://www.mathsisfun.com/combinatorics/images/permutation-no-repeat.png)          (No repetition, order matters)

Combination with repetition (http://www.mathsisfun.com/combinatorics/images/combinations-repeat.png) (Repetition allowed, order doesn't matter)

Combination without repetition             (http://www.mathsisfun.com/combinatorics/images/combinations-no-repeat.png)  (No repetition, order doesn't matter)

where n is the number of things to choose from, and you choose r of them

Hope this helps

Answered Sun 4th March, 2012 @ 17:47 by mathsxx