thanks for the response! Your point about the independent/dependent variables is kind of what I realized as I was answering the question, and made me feel better about the goofy 1/m answer.

Makes sense! Again, these are all really elementary but if you can help me with the concepts along with the answers I'd really appreciate it.

- In 1996, the average donation to the Help Way was $225 with a standard deviation of $45. In 1997, the average donation was $400 with a standard deviation of $60. The donations in which year show a more dispersed distribution?

- A researcher has obtained the number of hours worked per week during the summer for a sample of fifteen students [40, 25, 35, 30, 20, 40, 30, 20, 40, 10, 30, 20, 10, 5, 20]

Using this data set, compute the standard deviation. The data totals 380 and the mean is 25, the formula I have is (x-mean)*2 / n-1 to get the sample variance but I don't think I'm in the ball park.

Lastly,

A sample of charge accounts at a local drug store revealed the following frequency distribution of unpaid balances.

Unpaid balances Frequency
10-29 5
30-49 10
50-69 6
70-89 9
90-109 20

The class marks are 19.5, 39.5, 59.5, 79.5 and 99.5 which then mulitiply by the frequencies and suming equals 3555/45 equals 79. Again the formula for calculating the sample variances confuses me with the sum(x-M)*2/n-1 formula.


PLEASE HELP!!! I'd really appreciate it!

Using the formula 19.5-79*2 I'm getting $3,540.25, then $1560.25, ect. Am I calculating that correctly?

Actually my math really sucks it's 3555/50 for 71.1 for the mean which will make them even sloppier numbers.

Sorry for the nonsense, I just feel ******ed.

i dont have time for a detailed answer now (lot of work piled up tonight) but for sure sample varience is sum (x-mean)^2 / n-1
so its squared. not *2.
For the first question, i dont know how we "measure" a distribution being dispersed. But clearly whoever is asking you this questions wants to check if you understand that a distribution with a way higher mean then some other, but only a bit higher stnd deviation will look a lot less dispersed. so i am sure you are supposed to answer that the 225/45 one is more dispersed.
Annnyhow. I suck at statistics anyways in a sad way, so maybe other people will offer more help.

Possibly a very simple question, couldn't find the answer tho.

How do you simplify this, (Square root of A) - (Square root of B), Divided by (Square root of A) + (Square root of B) ??

Thanks

Multiply by 1 : (sqrt a - sqrt b) / (sqrt a - sqrt b)

Just learned how to solve second order differential equations in the form of series expansions, the first time I've been impressed by math.

This and Laplace transforms were my favorite parts of my intro ODE course. Can you tell I'm not an analyst?

This is my final plea for help, hopefully On the above problems can someone please tell me if the researcher problem's standard deviation is 11.34 and the variance for the drug store problem is 1168.62. I have to submit this online quiz by 1pm tomorrow and want to make sure I'm not way off track.

Your standard deviation for the researcher problem looks correct. I'm not entirely sure of the other one.

Isn't the standard deviation just sqrt(120)=10.95445 for the researchers problem?

Just using std^2 = variance = E[X^2]-E[X]^2 = 745-25^2 = 120

The result for the drug store intuitively feels too large, but I don't know enough about calculating the variance of ranges to really give you a definitive answer, sorry.

Hi,

I have an interview for a job on Wednesday. The first stage was just competency and I aced it and they said they'd inform me on Monday when interview would be the following week. So today I get told they are only interviewing on Wednesday and Thursday this week because of urgency.

I did 1 module of chemistry in year 1 of uni but that was 4 years ago now and I am required to take a Chemistry test.

The job is for a patent editor for a drug company and the specs state you need a knowledge of organic chemistry and chemical nomenclature.

So far I'm just gonna learn the basic rules for mechanisms very quickly in case stuff comes up and learn this: http://en.wikipedia.org/wiki/IUPAC_n...anic_chemistry

Does anyone have any suggestions on the areas of organic chemistry I should focus on because I have very little knowledge of Chemistry at the moment.

Buying an organic chem textbook would be your best bet, but you won't be able to learn much in just a few days.

I'm looking to generate random numbers within a range that follows one of the two following graphs...

Question 1
I'm looking for a way to solve for two curves regardless of x_max. The first is simple, y=1+(9/x_max)*x

The second needs to be some form of y=x^2+1 and pass through (x_max, 10)




Question 2
Very similar, but a more complicated curve. I toyed with ln(x) and cube root of x, but couldn't get quite the control I wanted.




Thanks in advance!

Find an equation for the inverse of h(x) = f(cx), where 'c' cannot equal zero.

Attempt at solution:

if y = f(cx) then its inverse would be x = (f^-1(y)) / c in which case

h^-1(x) = (f^-1(x)) / c

Is the algebra correct here? How would we explain this conceptually?

Yes this is correct. Conceptually, I'd say that, starting with x, we multiply by c, and then apply f to get y. So to undo this, we apply f^(-1) and then divide by c. Or, in MSPaint terms:

Hey thanks the diagram makes sense. Sorry I wasn't clear but by conceptually I meant graphically in that, how can we explain this in terms of f(x) or f^-1(x) stretching and compressing by factors of 'c'?

Some Group Theory: (-= is does not equal)

Let G be a non-abelian group containing elements a, b and satisfying:
1) a-=e-=b
2) ab(a^-1)= b^2

Show b^2^k= (a^k)b(a^-k) for any positive integer k

I know that i need to prove this by induction.

Base case k=1 is true as given
Inductive Hypothesis: Assume k=n is true, show that k=n+1 is also true

b^(2n+2)=(a^n+1)b(1^-n-1)

(b^2n)(b^2)=(a^n)ab(a^-n)(a^-1)

substituting for b^2
(b^2n)aba^-1=(a^n)ab(a^-n)(a^-1) (multiply by a on the right on both sides)
(b^2n)ab=(a^n)ab(a^-n)

this is as far as I have gotten without going in circles. I am not sure if I am on the right track, but if I can show this is true then I have it true for all natural numbers including n=k my base case.

!= is the standard not equal sign.

I'm pretty sure you want b^(2^k), as opposed to (b^2)^k = b^2k. Induction should be easy then.

yea i wrote it is B^2^k same thing...if you follow my work I wrote B^2k so the same thing. The problem is I am still fairly new to proofs hence way out of my league here. Can you look over my work and tell me if I am missing something?

you should reread banzai-'s post.

I am confused now, the question is written without parenthesis b^2^k, so if it is in fact b^(2^k) how does that make induction easier?

edit: looking over my work, it is b^(2^k) as another part of this question clarifies it (unrelated to this question though). so now I have:

b^(2^(n+1))=a^(n+1)ba^(-n-1)

=(a^n)ab(a^-n)a^-1

I am confused about what I can do with this now. Any help would be great thanks.

start by not assuming what you're trying to prove. Go through the induction.

k=1?
Assume for k=n. Prove for n+1.
Can you write b^(2^(n+1)) in terms of b^(2^n)?