Oracle Database Discussions

In my database design and implementation module I'm at the implementation stage. I've set up all of my tables with PK and FK constraints and I'm wondering if you can enforce min and max column constraints. One of the rules of my DB is for my staff table there has to be a minimum of 10 and a maximum of 50, how would I enforce this rule as a constraint on the staff table or isn't this possible?

We have only been learning database design and SQL fundamentals so I don't think I'd be allowed to use triggers or procedures.

Many thanks

Mike