IF & DATEDIFF - 3 Status Help with my function Please

[HelpmeRhonda]

I have a status Column with 3 texts: Completed, In Progress, Not Started. 

I would like to pull for both "In Progress" and "Not Started" or pull for all but "Completed".  

This works but what would I need to add to do what I need?

Days Open = if(

([TASK_STATUS]="In Progress"),

DATEDIFF(TEST[TASK_FINISH],TODAY(),DAY)& "",

""

)

[HelpmeRhonda]

Thank you so much for you help! 

[lbendlin · Accepted solution]

[TASK_STATUS]<>"Completed"

or

[TASK_STATUS] IN {"In Progress","Not Started"}