If a Parameter contains Range Values, use the Minimum and Maximum functions to get the lower and upper bounds of the range.

You will need to create another formula. Here is a formula sample that is printed on a page header from one of my reports.

"For all Orders from " + ToText(Minimum ({?OrderDates}),"dd-MMM-yyyy") + " To " + ToText(Maximum ({?OrderDates}),"dd-MMM-yyyy")