Equation to extrapolate values

[markfitzw]

I have a table in Excel:

Project Value	Hours
10000	36
25000	68

If I inserted rows to show every hour between 36 and 68, what equation would extrapolate the corresponding Project Value values? An example of the new table would be:

Project Value	Hours
10000	36
?	37
?	38
?	etc.
?	66
?	67
25000	68

I figured out an equation to extrapolate from 0 hours to 36. It would be:

Project Value	Hours
=(0/36)*10000	0
=(1/36)*10000	1
=(2/36)*10000	2
etc.	etc.
=(34/36)*10000	34
=(35/36)*10000	35
10000	36

But this equation will not work when the base Project Value is not 0 (going from 0 to 10000). In my case, the base Project Value is 10000 (going from 10000 to 25000). I assume I somehow need to have a multiplier in the equation to convert down to a base of 0. Probably so it can be a percentage 0 to 100.

 

[Harry_the_cat]

If you are assuming a linear change, note that you have 68-36=32 steps between row 10000 and 25000 (an increase of 15000), so each step will be 1/32 of 15000.

 

[Deleted member 4993]

I have a table in Excel:

Project Value	Hours
10000	36
25000	68

If I inserted rows to show every hour between 36 and 68, what equation would extrapolate the corresponding Project Value values? An example of the new table would be:

Project Value	Hours
10000	36
?	37
?	38
?	etc.
?	66
?	67
25000	68

I figured out an equation to extrapolate from 0 hours to 36. It would be:

Project Value	Hours
=(0/36)*10000	0
=(1/36)*10000	1
=(2/36)*10000	2
etc.	etc.
=(34/36)*10000	34
=(35/36)*10000	35
10000	36

But this equation will not work when the base Project Value is not 0 (going from 0 to 10000). In my case, the base Project Value is 10000 (going from 10000 to 25000). I assume I somehow need to have a multiplier in the equation to convert down to a base of 0. Probably so it can be a percentage 0 to 100.

If you are working with excel - then use "trend line" in excel and it will give you the equation.

 

[markfitzw]

Thanks! I now have the equation (yes, I am assuming a linear trend).

The change in each step would be 1 divided by the maximum Hours minus the minimum Hours, times the maximum Project Value minus the minimum Project Value. So the constant equation for my example is:
= (1 / (68 - 36)) * (25000 - 10000)

Then for each succussive step, the previous Project Value needs to be added to this constant equation to calculate the increase. Thus, the equation for my example is:
= previousProjectValue + ((1 / (68 - 36)) * (25000 - 10000))

Obviously the syntax looks different in Excel.

Also, thanks for the "trend line" example. I briefly looked into that but I went with the custom equation. I will definitely explore this Excel feature in future.

Thanks again!

 

[Dr.Peterson]

I have a table in Excel:

Project Value	Hours
10000	36
25000	68

If I inserted rows to show every hour between 36 and 68, what equation would extrapolate the corresponding Project Value values?

One thing you should know is that what you are doing is not called extrapolating, but interpolating. Extrapolation means going outside the bounds of known data, whereas you are looking between the given values.