Automatic goal seek program

Does it have to be done by goal seek? It seems to me that the algebra involved is very simple, in this case, so that it will be much easier to solve the problem algebraically rather than try to automate goal seek. Correct me if I'm wrong but it looks like the problem is:

F(O2)=F(total)*y(O2)
Given F(O2) and y(O2), solve for F(total).

Then program that formula into your total flow cell. Is there more to the problem than that?

A few additional thoughts:

1) I am not real good with chemical balance problems, but it seems that they are mostly "solve a system of equations" type of problem. Even though the math is now more complicated than the original question, I would still tend to work through some of it. Many of these type of problems that I have done end up being "linear" equations, which means they can be solved using "Gaussian elimination" and/or "matrix inversion" which is easily automated in Excel using the built in MINVERSE() (and maybe other matrix functions) function.

2) If it really turns out that it must be solved using numerical methods, then Goal Seek can be automated in VBA using the Goal Seek method: https://msdn.microsoft.com/en-us/lib...ce.11%29.aspx# At this point I am assuming you are familiar with VBA. If not, then I would recommend that you review Excel's object model and other introduction to VBA type resources. It is often easiest to start with the macro recorder, record yourself running the Goal Seek manually, then use that as the "core" of your VBA procedure. Depending on the level of automation required, you may want to associate the procedure with the calculate event, if you are familiar with event procedures.

3) I tend to prefer Solver over Goal Seek, just because it is a more robust utility. Solver uses the same Newton-Raphson type algorithm that Goal Seek does, but has other options as well. Solver can be programmed into VBA as well in a similar fashion.

4) If you are familiar with the NR and other numerical algorithms, it is possible to program those into a spreadsheet and bypass the use of Goal Seek. Many times, if I want to automate a calculation like this, I will prefer to program my own NR algorithm rather than code goal seek into VBA.

As you can see, I tend to use "automate Goal Seek using VBA" as my last resort. It can be done, and the help file contains examples. We also have many examples around the forum. Since I try to avoid it, I am not very good at coding Goal Seek in VBA (though it doesn't seem that difficult). If this is the direction you would like to go, then let us know where we need to start.