Question

Who can help me with statistics?

Answer 1

Yes!

Answer 2

can you help?

Answer 3

Working on it

Answer 4

Im afraid d00d

Answer 5

Its taking time for me, Sorry 'bout that

Answer 6

Sorry, statistics is out of my area...

Answer 7

Yoou should probably try the statistics section.

Answer 8

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

Answer 9

nobody helps me in statistics section

Answer 10

The average should be just (0.15) * 235

Answer 11

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

Answer 12

Okay I mean (0.15)*205

Answer 13

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

Answer 14

what about the second one

Answer 15

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

Answer 16

what is x and n?

Answer 17

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

Answer 18

27/235 ?

Answer 19

is that right?

Answer 20

sorry I gotta go

Answer 21

please help me out

Answer 22

last one

Answer 23

isn't the mean just 15% of 205 ?

Answer 24

im not sure

Answer 25

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

Answer 26

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

Answer 27

so how should I find it

Answer 28

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

Answer 29

standard deviation is what @wio wrote as well

Answer 30

I don't understand last one

Answer 31

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

Answer 32

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

Answer 33

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

Answer 34

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

Answer 35

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

Answer 36

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

Answer 37

wait

Answer 38

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

Answer 39

i have this formula

Answer 40

i need to use that formula

Answer 41

i have no idea what p hat means

Answer 42

so for the n should I use 205?

Answer 43

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

Answer 44

thank you anyway

Answer 45

p hat actually equals to = x/n

Answer 46

I dont understand b first question
also c

Answer 47

sorry not my area

Answer 48

are u there?

Answer 49

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)

\[E[X/n] =\sum_k \frac{k}{n} f(k) = \frac{1}{n}\sum_k k f(k) = \frac{1}{n}E[X] \]

Answer 50

actaully for the second one we have to use p hat

Answer 51

do you know p hat?

Answer 52

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

Where X i the number of lefties and n is the total number of students in the class.

Answer 53

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

Answer 54

cuz i dont really know how to find it ?

Answer 55

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

Answer 56

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

Answer 57

so you mean 27 / 205 ?

Answer 58

did you see question b ?

Answer 59

it asks for mean and standard deviation

Answer 60

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.

Answer 61

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.

Answer 62

can you solve it ? cuz i cant