working backwards from weighted averages

[moony]

Hello,

I have 3 numbers that were given to me that are $/SF weighted averages. The developer didn't provide the weight factored into calculating each average.

[TABLE="width: 500"]
<tbody>[TR]
[TD][/TD]
[TD]Total Project $/SF Average[/TD]
[TD]1st Product $/SF W. Avg[/TD]
[TD]2nd Product $/SF W. Avg[/TD]
[TD]3rd Product $/SF W. Avg[/TD]
[/TR]
[TR]
[TD][/TD]
[TD]379[/TD]
[TD]398[/TD]
[TD]339[/TD]
[TD]289[/TD]
[/TR]
[TR]
[TD]% of Weight[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
</tbody>[/TABLE]

What I would like to find out is how I can find the correct weight to each product's weighted average so as to arrive at the Total Project $/SF Average of 379.

Thanks

 

[Eric W]

Sorry, this is the mathematical equivalent of 1 equation, 3 unknowns. This means that there are an infinity of solutions. I set up Solver to find some of them:

40, 1, 8
190, 88, 1
55870, 26536, 1

No particular order or pattern. You'll probably need to call the developer.

 

[moony]

ahhh, got it. i wish my fundamental math skills were stronger, even after taking all the calculus i have taken...

i appreciate your help

 

[moony]

hmm... I may have forgotten a key detail: what about the SF of each product? If you knew that Product (1) 1416 SF, Product (2) 486 SF, and Product (3) 3,500 SF and the total cost is 18,372,997, would that help?

 

[moony]

Probably my food coma from lunch.... but there are 25 units of Product (1), 8 of (2), and 1 of (3). With a quoted gross SF of 58,268

 

[moony]

I reached out to the developers, but I fear they won't get back to me until Monday.
They provided another Total Project Cost that included some other fees. They weren't supposed to include those in the weighted averages because of how those fees are structured, but it seems they may have. If that's the case, the number to use shouldn't be that ~18mm, but 22,096,604.