Turn on thread page Beta

Edexcel S3 Help!!! watch

Announcements
    • Thread Starter
    Offline

    0
    ReputationRep:
    When are you meant to combine the cells, in the chi squared questions, also how do you work out the degree of fredoms??

    for example the question is below:

    what i did; d.o.f = 5-1-1 = 3

    -1 for working out mean
    -1 (as you always have to minus 1 that what i have been told :confused: )

    h0= poissonly distributed
    h1= not poissonly distributed

    then i worked out sum of oi^2/ei -n = 106.255-100= 6.256

    X^2(5%)(3) = 7.815

    6.256 < 7.815

    reject h1 as mangers claim is correct data is poissonly distributed


    but ms says my d.o.f is wrong and my sum of oi^2/ei -n is also, as i have to combine the last two cells? why is this????


    Click image for larger version. 

Name:	Capture.PNG 
Views:	327 
Size:	28.1 KB 
ID:	284464

    Click image for larger version. 

Name:	Capture2.PNG 
Views:	317 
Size:	63.4 KB 
ID:	284465
    Offline

    14
    ReputationRep:
    You should combine cells so that none of them are less than OR EQUAL to 5. I don't know why; but the textbook emphasizes on this bit at least.

    You minus 1 for calculation of the mean and -1 because of the additive constraint. That the sum should add up to a certain value so the last cell or a single cell has no degree of freedom.
    Offline

    0
    ReputationRep:
    Jan 2006 Question 5

    Why should you use n=80 for the girls here?

    5. Upon entering a school, a random sample of eight girls and an independent random sample of eighty boys were given the same examination in mathematics. The girls and boys were then taught in separate classes. After one year, they were all given another common examination in mathematics.

    The means and standard deviations of the boys’ and the girls’ marks are shown in the table.

    Examination marks
    Upon entry After 1 year
    Mean Standard deviation Mean Standard deviation
    Boys 50 12 59 6
    Girls 53 12 62 6

    You may assume that the test results are normally distributed.

    (a) Test, at the 5% level of significance, whether or not the difference between the means of the boys’ and girls’ results was significant when they entered school.
    (7)
    (b) Test, at the 5% level of significance, whether or not the mean mark of the boys is significantly less than the mean mark of the girls in the ‘After 1 year’ examination.
    (5)
    (c) Interpret the results found in part (a) and part (b).
    (1)
    Offline

    14
    ReputationRep:
    Maybe a typo. The y is missing.

    Posted from TSR Mobile
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: May 16, 2014

University open days

  • University of East Anglia
    All Departments Open 13:00-17:00. Find out more about our diverse range of subject areas and career progression in the Arts & Humanities, Social Sciences, Medicine & Health Sciences, and the Sciences. Postgraduate
    Wed, 30 Jan '19
  • Aston University
    Postgraduate Open Day Postgraduate
    Wed, 30 Jan '19
  • Solent University
    Careers in maritime Undergraduate
    Sat, 2 Feb '19
Poll
Brexit: Given the chance now, would you vote leave or remain?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.