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Statistics S1 post your doubts here

Sarmad Paracha

Sarmad Paracha

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Can anyone help me with continuity correction plz....i'm confused when to add or subtract those limits.....plz help.....giving As this 22nd
 
Talha Irfan

Talha Irfan

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Talha Irfan

Talha Irfan

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IGCSE13 said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s11_qp_62.pdf in question 5 i do we have to use class boundaries and in iii I don't get when do we have to subtract from the total can someone please hell me
Click to expand...
Yes, we have to use class boundaries or define these classes in terms of x<=k
For example, 1-20 is x<=20 similarly 41-50 will be x<=50 and corresponding cumulative frequency will be written with each of them below and then graph will be drawn for example for x<=20 you have cf = 10 so you have one co-ordinate as (20,10). Now note one thing, the reason why are we not aligning the classes is because the random variable here is rooms and rooms are discrete you can't have 1.5 rooms right, so due to the random variable being discrete we do not align the classes by taking average. However if mean was asked then we have to do so. Second part of query : The questions when says above or over any number for example in this question over 30 rooms was asked so from graph you got days for rooms less than 30 so for more you have to subtract from total to get the upper part.
 
I

IGCSE13

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Talha Irfan said:
Yes, we have to use class boundaries or define these classes in terms of x<=k
For example, 1-20 is x<=20 similarly 41-50 will be x<=50 and corresponding cumulative frequency will be written with each of them below and then graph will be drawn for example for x<=20 you have cf = 10 so you have one co-ordinate as (20,10). Now note one thing, the reason why are we not aligning the classes is because the random variable here is rooms and rooms are discrete you can't have 1.5 rooms right, so due to the random variable being discrete we do not align the classes by taking average. However if mean was asked then we have to do so. Second part of query : The questions when says above or over any number for example in this question over 30 rooms was asked so from graph you got days for rooms less than 30 so for more you have to subtract from total to get the upper part.
Click to expand...
But in the marking scheme the points used were (20.5,10)..
 
ZaqZainab

ZaqZainab

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IGCSE13 said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w11_qp_62.pdf in q4 iv what is the interval used
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the intervals given already in the question
you find frequency by 0-0 20-0 50-20 100-50 160-100 210-160 220-210 u will have 0,20,30,50,60,50,10
and the class width is 20-0 30-20 40-30 45-40 50-45 60-50 70-60 you will have 20,10,10,5,5,10,10
Frequency Density= F/class width 0/20 20/10 30/10 50/5 60/5 50/10 10/10----> 9,2,3,10,12,5,1
 
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IGCSE13

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ZaqZainab said:
the intervals given already in the question
you find frequency by 0-0 20-0 50-20 100-50 160-100 210-160 220-210 u will have 0,20,30,50,60,50,10
and the class width is 20-0 30-20 40-30 45-40 50-45 60-50 70-60 you will have 20,10,10,5,5,10,10
Frequency Density= F/class width 0/20 20/10 30/10 50/5 60/5 50/10 10/10----> 9,2,3,10,12,5,1
Click to expand...
It is given in the question <20 doesn't mean from 0-19 since 20 is not included
 
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IGCSE13

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ZaqZainab said:
they have not asked you class width here have they?
the one i answered was for class width here they just want marks which is x
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But I need to have an interval from which I would obtain the midpoint to calculate the mean
 
A

_Ahmad

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Exo_luhan said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s12_qp_61.pdf

Q6 ii plz ne1?
Click to expand...

1 sd from the mean = 1 sd below or 1 sd above the mean
since you have the sd= 3.156 and mean 9.95
you can find the probability ie
P(X less than 9.95-3.156) or P(X greater than 9.95+3.156)
=P(X less than 6.794) or P(X greater than 13.106)
=P(Z less than 6.794-9.95/3.156) or P(Z greater than 13.106-9.95/3.156)
=P(Z less than -1) or P(Z greater than 1)
=P(Z less than -1) or 1-P(z less than 1)
=ϕ(-1) + 1-ϕ(1) (or means +)
=1-ϕ(1) + 1-ϕ(1)
=2-2ϕ(1)
=2-2(0.8413)
=0.3174

1000*0.3174=317.4
= 317
 
Talha Irfan

Talha Irfan

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IGCSE13 said:
But in the marking scheme the points used were (20.5,10)..
Click to expand...
The mark scheme also says ACCEPT (20,10) (40,42) etc and logically I cannot think of assigning a non discrete number to a discrete variable
 
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