Crystal Report 8.5 Sub-Report question

I am quite new to Crystal Reports hence this simple question.

I am trying to create a report for a call center that would display the following for a given agent:
1.) Number of cases created during a date range (CASE_TABLE.CREATED_DATE)
2.) Number of cases closed during the same date range (CASE_TABLE.CLOSED_DATE)
3.) Number of cases that are outstanding till the date of report.

I created 3 reports
1.) Count of Case_Created for cases created- prompts for agent, created_from_date, created_to_date
2.) Count of Case_Closed for cases closed- prompts for agent, closed_from_date, closed_to_date
3.) Count of Case_Outstanding for cases open- prompts for agent.

Each of them individually run fine.

I created a new report using Case_Created as primary report and Case_Closed & Case_Outstanding as sub-reports with proper linkages.

When I try running the report, it prompts me for prompt values 3 times - once for Case_Created, once for Case_Closed and once for Case_Outstanding though the values for each are same.

How do I get rid of the 2 extra prompts from appearing and instead use the values specified in the first prompt for running the sub-reports?

(I was able to get over this using a single query with Unions and then grouping the data as per my needs. Yet I would still like to know if there is a way to get over this.)

Thanks.