Finding the number of days to bring up an average (without using goal seek)

[Baghtal]

Hello,

I've been looking around for an hour or so and have found a couple of great ideas about how to bypass goal seek for interest and payment items, but i can't figure out how to adapt them to my scenario... If anyone can help out I'd appreciate it!

I'm looking for a way to solve for the Number of days needed to reach our goal without an outage (the number in B2).

Row 45 is setup with A = counter number, B = Today(), c: Days since b44 (last outage) and d45=average of the days between outages (Column C including row 45).

My Question: How to do I setup a formula to figure out what C45 needs to be without using goal seek or Macro's?
(This excel chart is viewed by many people in my department and it would make my life much easier if i didn't have to explain to them why they need to trust macro's for the worksheet )

The numbers in Row 2, are actually pointers to the rows below [i.e. A2 =VLOOKUP(TODAY(),B4:C1000,2)] so it is kept up-to-date dynamically by the TODAY function of the most current filled cell in column B. I am looking for a way to dashboard the top rows with the latest outage information filled in the section below without manually figuring it out every time.


Hopefully that all made sense. Thanks for looking

 

[Steve=True]

Back to Algebra II

25= Sum(Old Data)+X
Count(old Data)+1

Solve for X

25*(Count(old Data)+1)-sum(old Data) = X

x = amount needed to reach 25