In 2010 there is a marked change in the way that Project calculates the tasks there is now an option that decides whether you may (By default) have automatic or manual scheduling for your tass the full meaning will become clear later but to briefly explain. In earlier versions scheduling was automatic by default which meant that if you changed the assigned resources for a given task then the task duration would change if the effort of the resource was reduced then the duration would automatically lengthen. As you will see later there options will appear for each task to.
