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.
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.
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
