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Logarithm calculations in Excel

Adarsh S

New Member
Can we solve this equation in Excel to find out the value of "ks"?

-9.782 = log ( 0.0000255 + ( ks / 3.71 ))

GraH - Guido

Well-Known Member

Since this was not answered yet, I'll give it a go. However far out of my comfort zone as I'm not familiar with LOG, nor with goal seek, but that seems to return a result:
Enter the known values in cells and a dummy value for "ks", then run goal seek and set target value by changing "ks" cell. It takes a long time, but this comes out.

Else be a little more patient....

Peter Bartholomew

Well-Known Member
= 3.71 * ( 10^(-9.782) - 0.0000255 )
is the same formula as that given by @vletm.
I would also observe that 10^(-9.782) is so close to being zero that it is the other term that counts, so
= - 3.71 * 0.0000255
provides a good approximation to the correct solution.