# Basic logarithm

I'm very new to logarithm.
I've got homework to solve a ques using logarithm i.e multipication of 9356 by 0.396. And i've done it in following manner

9356*0.396
=log 9356 + log 0.396
=3.9711-1.4023
=2.5688

I know i've done it in a wrong manner as the ans is wrong. I'm very new to it. I just know how to see logarithmic table and know basic formulae only. I just want to know the procedure to do such questions

Mark44
Mentor
I'm very new to logarithm.
I've got homework to solve a ques using logarithm i.e multipication of 9356 by 0.396. And i've done it in following manner

9356*0.396
=log 9356 + log 0.396
=3.9711-1.4023
=2.5688
It should be obvious that you've done something wrong, since you have 9356 * .396 being equal to 2.5688.

What you're really doing, but not showing, is taking the log of 9356 * .396.

There's another error -- log(.396) is not -1.4023.
I know i've done it in a wrong manner as the ans is wrong. I'm very new to it. I just know how to see logarithmic table and know basic formulae only. I just want to know the procedure to do such questions

Then what to do sir, this is my first ques of such a kind.
I've to calculate using logarithm. Please tell me the first step, rest of all i think i'll do myself.
Should i've to do log9356*log0.396?

Hey this time i got right answer.
I do it in this way
I assume ans to b x then,
Log(9356*0.396)=log x
3.5688=log x
x=antilog 3.5688= 3705
And i thnk this is right

Mark44
Mentor
You should have
log(9356*0.396)
= log 9356 + log 0.396
Now continue from there.

When you're done, you will have a number that is the logarithm of (9356*0.396).

Presumably the problem wants you to find 9356*0.396, which is easy enough to do using multiplication (by hand or using a calculator), but more difficult if you have to use logs to get it.

Let's call your answer L, where L = log(9356*0.396). To find (9356*0.396), exponentiate each side.
L = log(9356*0.396)
<==> 10L = 10log(9356*0.396)

Hopefully, you know enough about the properties of logs to be able to simplify the right side.

HallsofIvy
Homework Helper
Are they still teaching the use of logarithms for problems like that? With calculators as common as they are now, I would think using logarithms for multiplications and divisions would be outmoded.

(I am reminded of a science fiction story, I think by Isaac Asimov, taking place hundreds of years in the future, in which an engineer whips out his slide rule!)

Are they still teaching the use of logarithms for problems like that? With calculators as common as they are now, I would think using logarithms for multiplications and divisions would be outmoded.
Not in electronics. Logarithms are still used extensively in electronics as dB. I use them nearly every day.

(I am reminded of a science fiction story, I think by Isaac Asimov, taking place hundreds of years in the future, in which an engineer whips out his slide rule!)
A good example of doing multiplication and division by adding and subtracting logarithms.