Trouble with Sigma HW?

posted Nov 10, 2011, 6:24 AM by   [ updated Nov 10, 2011, 6:41 AM ]
#8 and #9 are reviews from Algebra 1:  
#8 nCr is probability- it's a combination.  Follow the link for a reminder.
#9 "!" means factorial.  Follow the link for a reminder.

#10, this is a challenge, so I won't take off if you skip it- but you should still try it.  plug in  everywhere you see an "i".    Just write it out, you don't have to evaluate (add) it.
For example: