Today we worked on problems where we have to decide either Permutations or Combinations to solve the problem.
Good examples were
P122 Example #1 and P152 Example #1
Here is a flowchart to help you to decide when to use Perms and when to use combs.

HW 

P126 # 1,2,5,6,7,10

and

P159 #2-10, 12