How do I calculate values from a chart?

[brooklynite]

Newbie here! So please be kind if I am posting in the wrong forum!

I have a series of numbers (X and Y) from which I create a chart from as shown on the attached Excel spreadsheet. The chart is the smooth line type available in Excel.

The question is, how do I find the Y value corresponding to a given X? Basically if X is given I need to be able to calculate the corresponding Y.

Thank you all for your HELP! I greatly appreciate any assistance as I am currently stuck in what I am doing and need to get this solved!

[pike]

The two formulae could be

if x<=55 , y=0.015x^2-1.643x=43.43,y=-0.033x+1.279
hope it helps

[pike]

Its best fit

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[yurttas]

Newbie here! So please be kind if I am posting in the wrong forum!

I have a series of numbers (X and Y) from which I create a chart from as shown on the attached Excel spreadsheet. The chart is the smooth line type available in Excel.

The question is, how do I find the Y value corresponding to a given X? Basically if X is given I need to be able to calculate the corresponding Y.

Thank you all for your HELP! I greatly appreciate any assistance as I am currently stuck in what I am doing and need to get this solved!

Your file attached below.

.

[brooklynite]

Your file attached below.

.

Thank you yurtass for the file. The formula you created seems to be a "linear interpolation". Unfortunately in most of my data samples (I am trying to find one now) a linear interpolation will result in numbers that are way off. Can this be done using the same method that Excel uses to create a non-linear curve just like the one shown in my file? Especially that I will need numbers OUTSIDE the range too so I guess it would be EXTrapolation.

[brooklynite]

Its best fit

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It kind of works below 40 but above that it starts to distort a little bit.

Doesn't Excel actually give us the values it uses to produce the smooth chart? What is the formula that it uses?

[yurttas]

Thank you yurtass for the file. The formula you created seems to be a "linear interpolation". Unfortunately in most of my data samples (I am trying to find one now) a linear interpolation will result in numbers that are way off. Can this be done using the same method that Excel uses to create a non-linear curve just like the one shown in my file? Especially that I will need numbers OUTSIDE the range too so I guess it would be EXTrapolation.

Is this okey?


.

[pike]

Ok then you need to calculate m
with

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then to find b when x = 0
and use
y=mx+b for each line

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see attached work book

[brooklynite]

Ok then you need to calculate m
with

Please Login or Register  to view this content.

then to find b when x = 0
and use
y=mx+b for each line

Please Login or Register  to view this content.

see attached work book

I like the slope idea and thank you so much for the info. The y=mx+b is if I assume LINEAR transition in between. Can you help me get a y=ax^2+bx+c or some other second degree formula? I think that would be a lot more complicated...