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How many ways can you write two different letters, so that they are in alphabetical order? For example, AB and CT count, but ZA does not.

 Dec 26, 2019
 #1
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26 C 2 =325 ways such as:AB, AC, AD......AX, AY, AZ.......25 combinations. Then it continues with B such as BC, BD, BE.........BX, BY, BZ........for 24 combinations ........and so on.

 Dec 26, 2019
 #2
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Note that we  have   25  ways  to  have the combo   A_

Then 24 ways to have the combo  B_

 

So....the number of  combos is just the sum of the first  25  positive integers  =  

 

(25 * 26)  / 2  = 

 

25 * 13  =

 

325  ways

 

 

 

cool cool cool

 Dec 26, 2019

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