# 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 inV2=voltage outR1=Resistor 1R2= Resistor 2formulas are:V2=V1xR2/R1+R2V1=V2(R1+R2)/R2R1=R2(V1-V2)/V2R2=R1xV2/V1-V2Any 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 dayAdon

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#1
October 4, 2013 at 05:58:04
 This appears to be a homework assignmentand 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.MIKEmessage edited by mmcconaghy

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#2
October 4, 2013 at 06:44:18
 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. message edited by DerbyDad03

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#3
October 4, 2013 at 15:36:42
 DerbyDad03 makes an important point.Maybe your formulae were written like this:V1xR2--------R1+R2If 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 - thanksmessage edited by Derek

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#4
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: http://www.daycounter.com/Calculato... 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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#5
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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