Marking scheme for assignment 4

Q1a:  2 marks for right answer
      2 for explanation.
Q1b:  same as Q1a
Q2a:  same as Q1a
Q2b:  same as Q1a
Q2c:  same as Q1a
Q2d:  same as Q1a

Q3:  2 marks for computing the number of possible passwords
     2 marks for explaining the number of possible passwords
     1 mark for applying PHP to get the answer
     1 mark for explaining why this is correct (they don't have to
     explicitly cite the PHP, but should give some justification).

Q4:  2 marks for the recurrence relation
     2 marks for explanation   
     1 mark for initial conditions (no explanation of initial conds reqd)

Q5:  5 marks
Note:  if they use the theorems for solving homogeneous equations,
they don't have to prove the answer is correct (since the theorem was
proved in class), but then they should show their work (roughly like
what I wrote in the solutions).  However, if they just guess a
solution, they should justify it.

Total 40