Question 162709
<pre>
number of ways that two letters can be selected from {A, B, C, D} if order in the sample is to be considered. List the possible samples. 


Your answer is wrong because you cannot duplicate a member of a set, 
such as AA.  There is but one A to choose.  The permutations are 

AB
AC
AD
BA
BC
BD
CA
CB
CD
DA
DB
DC

4 place 2.   Permutations of 4 things taken two at a time.

Edwin</pre>