How many ways can you reorder the letters in the word "CAT"? 
Follow the handout on "combinations", where order
Choose 5 students' names and then write out all possible 2-person
groups. There are only 10 of them, because order doesn't count.
Discuss the "handshake" problem. Draw a box like this to show that this problem is similar to
picking 2 letters out of a word. The number of people in the group goes
in the first box, then after you choose one person to handshake with
another, the number of people available to handshake with him or her goes
in the second box.
Key idea: For 2-person groups,
when order doesn't count, you divide the number of permutations by
(Remainder of class) In-class
Hand out homework as students successfully complete the in-class