## yashar806 one year ago Who can help me with statistics?

1. yashar806

2. SandeepReddy

Yes!

3. yashar806

can you help?

4. SandeepReddy

Working on it

5. SandeepReddy

Im afraid d00d

6. SandeepReddy

Its taking time for me, Sorry 'bout that

7. calmat01

Sorry, statistics is out of my area...

8. calmat01

Yoou should probably try the statistics section.

9. SandeepReddy

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

10. yashar806

nobody helps me in statistics section

11. wio

The average should be just (0.15) * 235

12. SandeepReddy

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

13. wio

Okay I mean (0.15)*205

14. wio

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

15. yashar806

16. wio

$\hat{p} = X/n$

17. yashar806

what is x and n?

18. wio

As I said before $$n$$ is number of students. $$X$$ is number of lefties.

19. yashar806

27/235 ?

20. yashar806

is that right?

21. wio

sorry I gotta go

22. yashar806

23. yashar806

last one

24. satellite73

isn't the mean just 15% of 205 ?

25. yashar806

im not sure

26. satellite73

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

27. satellite73

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

28. yashar806

so how should I find it

29. satellite73

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

30. satellite73

standard deviation is what @wio wrote as well

31. yashar806

I don't understand last one

32. satellite73
33. satellite73

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

34. yashar806

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

35. satellite73

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

36. satellite73

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

37. satellite73

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

38. yashar806

wait

39. satellite73

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

40. yashar806

i have this formula

41. yashar806

42. yashar806

i need to use that formula

43. satellite73

i have no idea what p hat means

44. yashar806

so for the n should I use 205?

45. satellite73

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

46. yashar806

thank you anyway

47. yashar806

p hat actually equals to = x/n

48. yashar806

I dont understand b first question also c

49. campbell_st

sorry not my area

50. yashar806

are u there?

51. LikeLightning

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

52. yashar806

actaully for the second one we have to use p hat

53. yashar806

do you know p hat?

54. LikeLightning

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

55. yashar806

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

56. yashar806

cuz i dont really know how to find it ?

57. LikeLightning

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

58. LikeLightning

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

59. yashar806

so you mean 27 / 205 ?

60. yashar806

did you see question b ?

61. yashar806

it asks for mean and standard deviation

62. bynowSPAMER

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.

63. LikeLightning

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.

64. yashar806

can you solve it ? cuz i cant