Multiplying matrices



Hi, 

Currently in my high school mathematics course I'm studying
probability. The current topic is to do with transitional and state
matrices. The idea is given a passed probability it is possible to work
out the probability of a future event. From the text book is a simple
example which should explain what I'm trying to do. 

A sporting team has a success rate of 0.8 of winning given they won the
last game, and a 0.5 chance of winning considering they lost the last
game. The team won the last match so I enter the following into maxima:

A:matrix([0.8,0.5],[0.2,0.5]);
                                 [ 0.8  0.5 ]
(%o1)                            [          ]
                                 [ 0.2  0.5 ]
(%i2) B:matrix([1],[0]);
                                     [ 1 ]
(%o2)                                [   ]
                                     [ 0 ]
(%i3) C:A*B;

fullmap: arguments must have same formal structure.
 -- an error. To debug this try: debugmode(true);
(%i4) 

And as you can see when multiplying the matrices I get this error. Does
anyone have any ideas of what I'm doing wrong? 

Thank you very much,
Dan