Logarithms Thread

[dinosaur93]

Badly need help!
For clarifications, kindly show working out, tnx!

The expression is equivalent to?
a.
b.
c.
d.


How come my answer yields to:



The intensity of light reduced by 2% for each metre that a diver descend below the surface of the water. At what depth is the intensity of light only 10% of that at the surface?


In chemistry, the pH scale measure the acidity ( 0 - 7) or alkalinity (7 - 14) of a solution. It is a logaritmic scale in the base of 10. Thus a pH of 9 is 10 times more than alkaline that a pH of 8. If a solution has a pH of 7.6. How many times more alkaline is it than neutral water. Represent each given in the form of a logaritmic expression. Which has a pH of 7?
a. 0.6                      b. 1.09                  c. 3.98                  d. 12.18



A recent earthquake in Brazil measured 7.2 on the Richter scale. In 1960, the earthquake in Morocco measured 5.8. How many times more intense was the earthquake in Brazil compared to the Morocco quake?


The pH scale is a logarithmic scale. If bleach has a pH of 13, how many more alkaline is it than blood which has a pH of 8?




If , determine an expression for .



Determine the magnitude of an aftershock that is 200 times as intense as a eartquake of magnitude 3.7 on the Ritcher scale.



The population of rabbits is increasing by 70% every 6 months. Presently there are 200 rabbits.
Determine an expression for the number of months it will take for the population to reach 800.

[dinosaur93]

anyone?

[TrueTears]

log_{10} B = log_{10} (A/C^2)

[TrueTears]

log[(100x^3)/y] = log(100)+log(x^3)-log(y) = 2+3log(x)-log(y)

[Gaijin]

The population of rabbits is increasing by 70% every 6 months. Presently there are 200 rabbits.
Determine an expression for the number of months it will take for the population to reach 800.

I sort of guessed the first line:

200*((1.7)^(n/6))=800    where n is number of months after present time
(1.7)^(n/6)=4
n/6=log(4)base(1.7)
n=6*(log(4)base(1.7))

Then just solve for n (I hope its right...)




SOMEONE PLEASE TEACH ME HOW TO USE EQUATION EDITOR!!!.... :b

[b^3]

SOMEONE PLEASE TEACH ME HOW TO USE EQUATION EDITOR!!!.... :b

Here is a link for the LaTeX generator -> http://www.codecogs.com/latex/eqneditor.php
It's easier to type it up in there and copy it over.

To put it in a post, click the "pi" (latex) button in the post window. You should get two "tex" tags where you paste the code from the other page in.

e.g. for
you should have "y=\frac{(x-2)^{2}}{4}" between the tex tags.

[Gaijin]

SOMEONE PLEASE TEACH ME HOW TO USE EQUATION EDITOR!!!.... :b

Here is a link for the LaTeX generator -> http://www.codecogs.com/latex/eqneditor.php
It's easier to type it up in there and copy it over.

To put it in a post, click the "pi" (latex) button in the post window. You should get two "tex" tags where you paste the code from the other page in.

e.g. for
you should have "y=\frac{(x-2)^{2}}{4}" between the tex tags.

Thanks b^3, I'll have a play around with it.

[Gaijin]

The intensity of light reduced by 2% for each metre that a diver descend below the surface of the water. At what depth is the intensity of light only 10% of that at the surface?

I'll try and answer this also, don't think I need the equation editor for this one:

I=100-2*d   where I is intensity of light as a percentage and d is distance under the surface in metres
10=100-2*d
d=45m

Therefore light is at 10% intensity at 45m depth