Who can help me with statistics?

- anonymous

Who can help me with statistics?

- katieb

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- anonymous

##### 1 Attachment

- anonymous

Yes!

- anonymous

can you help?

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## More answers

- anonymous

Working on it

- anonymous

Im afraid d00d

- anonymous

Its taking time for me, Sorry 'bout that

- anonymous

Sorry, statistics is out of my area...

- anonymous

Yoou should probably try the statistics section.

- anonymous

it was long ago that i studied stats, try in statistics section

- anonymous

nobody helps me in statistics section

- anonymous

The average should be just (0.15) * 235

- anonymous

@wio 15% of the PEOPLE are lefties, not 15% of the seats

- anonymous

Okay I mean (0.15)*205

- anonymous

\[
n = 205 \text{ trials (number of students)}\\
p = 0.15 \text{ probability}\\
-\\
\mu = np \text{ mean}\\
\sigma =\sqrt{np(1-p)} \text{ standard deviation}
\]

- anonymous

what about the second one

- anonymous

\[
\hat{p} = X/n
\]

- anonymous

what is x and n?

- anonymous

As I said before \(n\) is number of students. \(X\) is number of lefties.

- anonymous

27/235 ?

- anonymous

is that right?

- anonymous

sorry I gotta go

- anonymous

please help me out

- anonymous

last one

- anonymous

isn't the mean just 15% of 205 ?

- anonymous

im not sure

- anonymous

yeah i am pretty sure that is what it is.
i don't really know any statistics

- anonymous

oh i didn't look @wio wrote the answer above

- anonymous

so how should I find it

- anonymous

find the mean? it is \(.15\times 205=30.75\)

- anonymous

standard deviation is what @wio wrote as well

- anonymous

I don't understand last one

- anonymous

http://www.wolframalpha.com/input/?i=sqrt%28205*.15*.85%29

- anonymous

i guess you are to assume that it is normally distributed, so using a normal table find the probability that \(X<27\)

- anonymous

in this case should I use 235 or 205 ? for total?

- anonymous

or rather change to a z score, that is my guess

- anonymous

the 235 is not important. there are 205 students, the mean is \(30.75\) and the standard deviation is about \(5.11\)

- anonymous

\(30.75-27=3.25\) and \(3.25\div 5.11=.636\) approximately, so find the probability using a normal table that \(X<-.636\)

- anonymous

wait

- anonymous

that is my guess anyway, i would not bet any money on it

- anonymous

i have this formula

- anonymous

##### 1 Attachment

- anonymous

i need to use that formula

- anonymous

i have no idea what p hat means

- anonymous

so for the n should I use 205?

- anonymous

yes that is \(n\) but i have no idea what p hat means, so i am useless at this point

- anonymous

thank you anyway

- anonymous

p hat actually equals to = x/n

- anonymous

I dont understand b first question
also c

- campbell_st

sorry not my area

- anonymous

are u there?

- anonymous

This is a problem where one can apply the binomial distribution.
\[f(k) = \frac{n!}{k!(n-k)!} p^{k} (1-p)^{n-k}\]
This is for when there are number of yes/no outcomes. If one yes has probability p for an individual outcome, this formula gives the probability of getting k yes outcomes out of n total outcomes.
In this case p would be the probability of a single student being left handed.
Now if k students are left handed, the proportion of left handed students is (let's call it y)
\[y = k/n\]
So what are the mean and variance of this?
well to find the mean of the binomial distribution (the mean value of the number of students who are left handed) we'd do
\[E[X] =\sum_k k f(k)\]
But now we have some proportion k/n, but the probability is the same, f(k)
\[E[X/n] =\sum_k \frac{k}{n} f(k) = \frac{1}{n}\sum_k k f(k) = \frac{1}{n}E[X] \]

- anonymous

actaully for the second one we have to use p hat

- anonymous

do you know p hat?

- anonymous

\[\hat{p} = X/n\]
Where X i the number of lefties and n is the total number of students in the class.

- anonymous

can you give me a number? i mean use b as an example?

- anonymous

cuz i dont really know how to find it ?

- anonymous

p hat and X are not the usual kind numbers. They are labels to represent a number which has different probabilities for different values.

- anonymous

For example X = k has the probability f(k) which I gave.

- anonymous

so you mean 27 / 205 ?

- anonymous

did you see question b ?

- anonymous

it asks for mean and standard deviation

- anonymous

In statistics and probability theory, standard deviation (represented by the symbol sigma, σ) shows how much variation or "dispersion" exists from the average (mean), or expected value. A low standard deviation indicates that the data points tend to be very close to the mean; high standard deviation indicates that the data points are spread out over a large range of values.
The standard deviation of a random variable, statistical population, data set, or probability distribution is the square root of its variance. It is algebraically simpler though practically less robust than the average absolute deviation.[1][2] A useful property of standard deviation is that, unlike variance, it is expressed in the same units as the data. Note, however, that for measurements with percentage as unit, the standard deviation will have percentage points as unit.
In addition to expressing the variability of a population, standard deviation is commonly used to measure confidence in statistical conclusions. For example, the margin of error in polling data is determined by calculating the expected standard deviation in the results if the same poll were to be conducted multiple times. The reported margin of error is typically about twice the standard deviation – the radius of a 95 percent confidence interval. In science, researchers commonly report the standard deviation of experimental data, and only effects that fall far outside the range of standard deviation are considered statistically significant – normal random error or variation in the measurements is in this way distinguished from causal variation. Standard deviation is also important in finance, where the standard deviation on the rate of return on an investment is a measure of the volatility of the investment.
When only a sample of data from a population is available, the population standard deviation can be estimated by a modified quantity called the sample standard deviation.

- anonymous

No, I did not mean 27/205. By X I did not mean the number of seats for left handed people. I meant the number of left handed people.
There are different probabilities for different numbers of left handed people.

- anonymous

can you solve it ? cuz i cant

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