Making a variable the subject of formula

[fasman]

Hi,
I am trying to solve this equation by making w thw subject of the formula. Help please !!

D/w = Mr/(1 - (1+r)^(-(n-w))

Thanks

[VBAhack]

Welcome to the forums. Pls clarify what you are trying to do. Is it to solve the equation for w using known values for the other variables?

[fasman]

Hi,

I am trying to make the formula look something like this so when I supply the variable apart from "w" I should be able to find what "w" is. I need the formula rearrnged:

w = ???????????

[VBAhack]

Unless there is some clever manipulation or substitution I don't see, I believe there is no way to get the equation into a closed form w = f(M,r,n,D). If you are just looking for the value of w for specific values of the other variables, you probably could use a numerical technique (e.g. Excel solver, Newton Raphson, etc.).

Perhaps someone else in the forum has a better answer.

[TBeck]

i agree with VBAhack..
Ive tried several techniques to isolate w and each time they are unsuccessful.
Is this a problem from some place that you are asked to solve and there is a known answer or do you need to use the equation to assign a value to w in a program?

[Code Doc]

D/w = Mr/(1 - (1+r)^(-(n-w))

First, make sure # left parentheses = # right parentheses. They don't. 4 <> 3.
So, as it stands, nothing can be solved.

[Rassis]

Because you can´t get the equation into a closed form w = f(M,r,n,D), as VBAhack pointed out, I suggest you use Goal-seek in Excel.

I attach an example.

Hope it helps.