help constructing decision tree

I need help in constructing a decision tree for something like the following data, and I need to predict SALARY (using ID3).

What I really need to know is how I calculate the entropy for each of the attributes DEPARTMENT, STATUS and AGE. I ony can find examples calculating the entropy where there are only two results to deal with (eg. PLAY and NOT PLAY, SUNBURNT and NON-SUNBURNT). In this case, the end results are 25-30K, 30-35K, 35-40K, etc.

Department Status Age Salary Count  

sales      senior  31-35  45-50K  30 
sales      junior  26-30  25-30K  40 
sales      junior  31-35  30-35K  40 
systems    junior  21-25  45-50K  20 
systems    senior  31-35  65-70K  5 
systems    junior  26-30  45-50K  3 
systems    senior  41-45  65-70K  3 
marketing  senior  36-40  45-50K  10 
marketing  junior  31-35  40-45K  4 
secretary  senior  46-50  35-40K  4 
secretary  junior  26-30  25-30K  6 

TIA. Received on Tue Oct 16 2001 - 04:19:00 CEST