Now, let's suppose you only want to choose a few letters out of your word.
For example, you only want to choose 2 letters out of the word "TABLE".
Here are all the ways to pick them:TA TB TL TE AT AB AL AE BT BA
BL BE LT LA LB LE ET EA EB EL
There are 20 pairs.
Is there a rule here too? Of course there is:
1. There are 5 ways to choose the first letter.
2. After you choose the first letter,
there are 4 ways to choose the
second letter.
So, the number of 2 letter permutations of the 5 letter word "TABLE" is 5 x 4 = 20

How about a general rule? Here it is:
If you have a word with "N" letters in it, and you only want to pick a few letters from it, then:
Number of letters you want 
Calculate: 
Example: TABLE N = 5 letters 
2  N x (N1)  5 x 4 = 20 
3  N x (N1) x (N2)  5 x 4 x 3 = 60 
4  N x (N1) x (N2) x (N3)  5 x 4 x 3 x 2 = 120 
Using factorials, this is:
P = N! / (N  M)!
where M is the number of letters you are selecting.
For our example of 3 letters out of the word TABLE, this becomes:
P = 5! / (53)! = 120 / 2! = 120 / 2 = 60 ways.
