Logarithms

[sirsoto]

Hello,

How can I divide a logarithm by a logarithm? For example, I would like to
make the following computation in one cell:

= log10(number) / log10(number)

I know I can take the log of the numerator in one cell and the denominator
in another, however, this is not what I want. Please advise

[Tim Williams]

=LOG10(A1)/LOG10(A2)

Tim

--
Tim Williams
Palo Alto, CA


"sirsoto" <[email protected]> wrote in message
news:[email protected]...
> Hello,
>
> How can I divide a logarithm by a logarithm? For example, I would like to
> make the following computation in one cell:
>
> = log10(number) / log10(number)
>
> I know I can take the log of the numerator in one cell and the denominator
> in another, however, this is not what I want. Please advise

[davidm]

If by Log10(number) you mean Log (number) to base 10, then

=Log(A1)/Log(B1) in your chosen cell.

[sirsoto]

Thanks for responding. I tried it but it didn't work. In cell A1, I typed
the following:

=log( ( ((300000*.05)+1) / (150*49) ) /log(1.05) )

i only put the spaces here for your ease of reading. The result should
equal a non-integer, 22.0918475.

I did it by hand, so i know this value is correct.

[Losse]

Did Excel give you an answer of about 0.027?

I tried it by hand and got around 0.027. I copied and pasted what you wrote without the spaces into Excel and got around 1.98. I entered the different sets of the problem individually into Excel and got the correct answer of 0.027 again.

[Losse]

Excel knows the correct order of operations. As soon as you close the )'s, the log entry is complete.
You can try:
=LOG(1+300000*0.05)/(150*49) /LOG(1.05)

to get the correct answer of around 0.27

[MrShorty]

Not sure how you got 22.1 as the answer. I can't come up with 22.1.

The correct answer as written is 1.98. log( ( ((300000*.05)+1) / (150*49) ) /log(1.05) )
=log( (15000+1) / 7350 / log(1.05) )
=log(15001/7350/log(1.05))
=log( 2.04 / 0.021) = log(96.3) = 1.98

Losse's interpretation of what you wanted does evaluate to 0.027, but note that he changed the groupings so it isn't the exact same formula as you posted.

log(15001)/7350/log(1.05)=
4.18/7350/.021=.027

I expect that, with all those parantheses, there is some confusion as to what exactly you want to take the logarithm of and what should not, and overall where the parantheses should be.

[Losse]

Why don't you post it again using brackets to distinguish the area for the log?

[l.a.]

here in Excel what are logarithms for? what specific jobs could this be
applicable to? thanx

[MrShorty]

l.a.: logarithms show up frequently in math, science, and engineering calculations. Basically, a logarithm is the "inverse" of exponentiation [10^3=1000, log10(1000)=3]. There are several good tutorials on logarithms on the internet - try putting "logarithm" into your favorite search engine.