Solved MS Excel - calculate unknown value

October 3, 2013 at 21:58:26
Specs: Windows 7
Greeting all,

If possible i need a little help with a formula in Excel, if someone can kindly offer some advice?

I require Excel to provide a 4th value of the missing field; If i know 3 of the other values.

V1=voltage in
V2=voltage out
R1=Resistor 1
R2= Resistor 2

formulas are:

Any help would be very much appreciated, as I'm not sure if MS Excel is possible of doing such.

Thanks kindly and wish you where ever you are a special day


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October 4, 2013 at 05:58:04
This appears to be a homework assignment
and as such we won't give you the answer,
but if you post the formulas you have tried,
we can point you in the right direction.


message edited by mmcconaghy

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October 4, 2013 at 06:44:18
✔ Best Answer
Are you sure you have your equations correct?

V2=V1xR2/R1+R2 is very different from V2=V1xR2/(R1+R2)

R2=R1xV2/V1-V2 is very different from R2=R1xV2/(V1-V2)

Are you sure that you aren't missing some parentheses?

Here's a hint on how to set up the Excel formulas:

Start with this set up in a spreadsheet:

        A            B           C
1      Term        Value       Result
2       V1
3       V2
4       R1
5       R2           

Since you know what mathematical relationship exists between the 4 variables, enter equations in Column C referencing the corresponding cells in Column B. In other words, wherever you have V1 in an equation, substitute B2 in your Excel formula.

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message edited by DerbyDad03

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October 4, 2013 at 15:36:42
DerbyDad03 makes an important point.

Maybe your formulae were written like this:


If so the top line is divided by the sum of R1 and R2, in other words when writing it on one line it should be V1xR2/(R1+R2)

Always pop back and let us know the outcome - thanks

message edited by Derek

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Related Solutions

October 4, 2013 at 16:39:38
thanks all for the replies, it's appreciated! and sorry for the equations error, as i typed them in as fast as possible without checking the post first before submitting.

What i am trying to achieve is to try and find the correct values for an electronic circuit, if i already know three of the values and have Excel display the 4th correct value.

It is not for an assignment, just for a quick way for me to get the values to design circuits.

so, say if i know the output voltage (V2) and both the resistors (R1 & R2) values i would like to use in the circuit, by typing into excel their values it would give me the input voltage (V1) value to power the circuit.

Sorry to say but i am a little vague with Excel and wondered whether it could do this as such.

I have found this website calculator at:

but is not able to do what I'm after. So i thought i could some how use the formulas i have provided (in their correct form - Thanks for pointing this out) and using Excels "cells" put it together in a small simple quick little package for myself.

Thanks for your responses and hopefully with your smart minds i can have a solution.

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October 4, 2013 at 20:19:41
I already gave you the steps required to write your formulas in response #2.

Do you know enough about Excel to write a formula? If not, I can give you some more details.

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