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SandeepReddyBest ResponseYou've already chosen the best response.0
Its taking time for me, Sorry 'bout that
 one year ago

calmat01Best ResponseYou've already chosen the best response.0
Sorry, statistics is out of my area...
 one year ago

calmat01Best ResponseYou've already chosen the best response.0
Yoou should probably try the statistics section.
 one year ago

SandeepReddyBest ResponseYou've already chosen the best response.0
it was long ago that i studied stats, try in statistics section
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
nobody helps me in statistics section
 one year ago

wioBest ResponseYou've already chosen the best response.0
The average should be just (0.15) * 235
 one year ago

SandeepReddyBest ResponseYou've already chosen the best response.0
@wio 15% of the PEOPLE are lefties, not 15% of the seats
 one year ago

wioBest ResponseYou've already chosen the best response.0
\[ n = 205 \text{ trials (number of students)}\\ p = 0.15 \text{ probability}\\ \\ \mu = np \text{ mean}\\ \sigma =\sqrt{np(1p)} \text{ standard deviation} \]
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
what about the second one
 one year ago

wioBest ResponseYou've already chosen the best response.0
As I said before \(n\) is number of students. \(X\) is number of lefties.
 one year ago

satellite73Best ResponseYou've already chosen the best response.0
isn't the mean just 15% of 205 ?
 one year ago

satellite73Best ResponseYou've already chosen the best response.0
yeah i am pretty sure that is what it is. i don't really know any statistics
 one year ago

satellite73Best ResponseYou've already chosen the best response.0
oh i didn't look @wio wrote the answer above
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
so how should I find it
 one year ago

satellite73Best ResponseYou've already chosen the best response.0
find the mean? it is \(.15\times 205=30.75\)
 one year ago

satellite73Best ResponseYou've already chosen the best response.0
standard deviation is what @wio wrote as well
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
I don't understand last one
 one year ago

satellite73Best ResponseYou've already chosen the best response.0
http://www.wolframalpha.com/input/?i=sqrt%28205*.15*.85%29
 one year ago

satellite73Best ResponseYou've already chosen the best response.0
i guess you are to assume that it is normally distributed, so using a normal table find the probability that \(X<27\)
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
in this case should I use 235 or 205 ? for total?
 one year ago

satellite73Best ResponseYou've already chosen the best response.0
or rather change to a z score, that is my guess
 one year ago

satellite73Best ResponseYou've already chosen the best response.0
the 235 is not important. there are 205 students, the mean is \(30.75\) and the standard deviation is about \(5.11\)
 one year ago

satellite73Best ResponseYou've already chosen the best response.0
\(30.7527=3.25\) and \(3.25\div 5.11=.636\) approximately, so find the probability using a normal table that \(X<.636\)
 one year ago

satellite73Best ResponseYou've already chosen the best response.0
that is my guess anyway, i would not bet any money on it
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
i need to use that formula
 one year ago

satellite73Best ResponseYou've already chosen the best response.0
i have no idea what p hat means
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
so for the n should I use 205?
 one year ago

satellite73Best ResponseYou've already chosen the best response.0
yes that is \(n\) but i have no idea what p hat means, so i am useless at this point
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
p hat actually equals to = x/n
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
I dont understand b first question also c
 one year ago

LikeLightningBest ResponseYou've already chosen the best response.0
This is a problem where one can apply the binomial distribution. \[f(k) = \frac{n!}{k!(nk)!} p^{k} (1p)^{nk}\] 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) \[E[X/n] =\sum_k \frac{k}{n} f(k) = \frac{1}{n}\sum_k k f(k) = \frac{1}{n}E[X] \]
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
actaully for the second one we have to use p hat
 one year ago

LikeLightningBest ResponseYou've already chosen the best response.0
\[\hat{p} = X/n\] Where X i the number of lefties and n is the total number of students in the class.
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
can you give me a number? i mean use b as an example?
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
cuz i dont really know how to find it ?
 one year ago

LikeLightningBest ResponseYou've already chosen the best response.0
p hat and X are not the usual kind numbers. They are labels to represent a number which has different probabilities for different values.
 one year ago

LikeLightningBest ResponseYou've already chosen the best response.0
For example X = k has the probability f(k) which I gave.
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
so you mean 27 / 205 ?
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
did you see question b ?
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
it asks for mean and standard deviation
 one year ago

bynowSPAMERBest ResponseYou've already chosen the best response.0
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.
 one year ago

LikeLightningBest ResponseYou've already chosen the best response.0
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.
 one year ago

yashar806Best ResponseYou've already chosen the best response.0
can you solve it ? cuz i cant
 one year ago
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