retrieve value from multiple matching records

[Rajat]

Project Master                                                                                         Task Allocation

ProjectID  projectName  Project Status                                                 Task ID   ProjectiD  Task status

  P1            A                                                                                           T1          P1           Completed

  P2            B                                                                                           T2          P1            In progress

  P3            C                                                                                           T3          P1            Completed

                                                                                                                T4          P2           Inprogress

                                                                                                                T5          P2           Completed

                                                                                                                T6          P2           In progress

I need to update "Project status" in Project Master in such a way that if any of the task of Project is in progress then we need to update "Project status"  as "In progress" othervise "Completed".

Can any one tell me, how to approach this problem.

I tried it with LookupValue(),but is works only for one matching record.But here are multiple matching record.