• Hi All

    Please note that at the Chandoo.org Forums there is Zero Tolerance to Spam

    Post Spam and you Will Be Deleted as a User

    Hui...

  • When starting a new post, to receive a quicker and more targeted answer, Please include a sample file in the initial post.

ln and exp functions

yaelcohen

Member
Hello,

I appreciate any clue to something that I can not understand (attached a file).

In the file, there is a column called VALUE with different values.
The LN column is a LN function for the values in VALUE.
To verify that LN is true, I checked it with the EXP function that presented in EXP column.

Now I took an average.
I found that the average of the VALUE column is 2975548 and the average of the LN column is (14.865).
But when I use the EXP function to the number 14.865, I found it is:
EXP (14.865) = 2857671

My question is why is there no match, why there is a difference between 2857671 and 2975548?

I hope I was clear with my question?
Thank you
 

Attachments

  • Question 40.xlsb
    9.1 KB · Views: 4
Hi ,

It is a question of maths.

Suppose we take just two numbers to start with ; the average of these two numbers , which we will call A and B , is :

=(A + B)/2

The logarithm of this average result is :

=LN((A + B)/2)

When you take the average of the logarithms of the two numbers , you are using the formula :

=(LN(A) + LN(B))/2

Mathematically :

LN((A + B)/2) is not equal to (LN(A) + LN(B))/2

because logarithms are not like ordinary numbers.

Narayan
 
Hi ,

It is a question of maths.

Suppose we take just two numbers to start with ; the average of these two numbers , which we will call A and B , is :

=(A + B)/2

The logarithm of this average result is :

=LN((A + B)/2)

When you take the average of the logarithms of the two numbers , you are using the formula :

=(LN(A) + LN(B))/2

Mathematically :

LN((A + B)/2) is not equal to (LN(A) + LN(B))/2

because logarithms are not like ordinary numbers.

Narayan

Thanks a lot!, long time since school :)
 
Back
Top