Crosstab query question

I want to create a crosstab query where I can get an average for a select number of row entries. In other words, let's say I have a database with three fields: days of the week, company name, hours worked. The row heading would be the days of the week, the column heading would be the company name and the values would be average hours worked. Now, let's say I just want the average for the group of Tuesday, Thursday and Friday instead of individual averages for each day. Is there a way to do this? Thank you.