Statistics as level cie question help please

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Universecolors
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I do know the answer and steps for part 1 , I have a problem in part 2 .

Esme noted the test marks, x, of 16 people in a class. She found that Σ x = 824 and that the standard
deviation of x was 6.5.
(i) CalculateΣ(x−50)andΣ(x−50) 2. [3]
(ii) One person did the test later and her mark was 72. Calculate the new mean and standard deviation of the marks of all 17 people. [3]


(i) Σ(x – 50) = 824 – 16 × 50 = 24
Σ(x − 50)^2 =712

ii) (ii) new mean = 896/17 (= 52.7)
712 + 22^2 /17- 24 + (72 − 50) ^2/17
new sd = 7.94


*i do NOT GET why u have to subtract 50 from 72 and can just someone explain the steps for me please , I need help
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old_engineer
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(Original post by Universecolors)

ii) (ii) new mean = 896/17 (= 52.7)
712 + 22^2 /17- 24 + (72 − 50) ^2/17
new sd = 7.94

*i do NOT GET why u have to subtract 50 from 72 and can just someone explain the steps for me please , I need help
I think it's just because you're finding the new Var(x), after the new score of 72 has been included, by calculating the new Var(x-50).

Var(x) = Var(x - 50) = Σ((x - 50)^2)/n - ((Σ(x - 50))/n)^2
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Universecolors
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(Original post by old_engineer)
I think it's just because you're finding the new Var(x), after the new score of 72 has been included, by calculating the new Var(x-50).

Var(x) = Var(x - 50) = Σ((x - 50)^2)/n - ((Σ(x - 50))/n)^2
Yes I do know that , but my question is Why is 72 subtracted from 50 , what is the reason , why is it like that ,
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Universecolors
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(Original post by old_engineer)
I think it's just because you're finding the new Var(x), after the new score of 72 has been included, by calculating the new Var(x-50).

Var(x) = Var(x - 50) = Σ((x - 50)^2)/n - ((Σ(x - 50))/n)^2
I am already familiar with the formula
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Universecolors
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I know how to solve the first one , but come someone explain the second one .

Esme noted the test marks, x, of 16 people in a class. She found that Σ x = 824 and that the standard
deviation of x was 6.5.
(i) CalculateΣ(x−50)andΣ(x−50) 2. [3]

(ii) One person did the test later and her mark was 72. Calculate the new mean and standard deviation of the marks of all 17 people. [3]

Answer;
i)Σ(x – 50) = 824 – 16 × 50 = 24
ii) Σ(x – 50)2 = 712

The answer for ii is s.d=7.94

Please help , I really don’t understand
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old_engineer
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(Original post by Universecolors)
Yes I do know that , but my question is Why is 72 subtracted from 50 , what is the reason , why is it like that ,
The usual reason for processing linearly shifted data rather than raw data is to reduce the size of the numbers involved in computation - especially the squared numbers. However, in this case the numbers are not huge so I suspect the question is just designed to check students' ability to cope with linearly shifted data (or coded data as it's often called).
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Universecolors
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(Original post by old_engineer)
The usual reason for processing linearly shifted data rather than raw data is to reduce the size of the numbers involved in computation - especially the squared numbers. However, in this case the numbers are not huge so I suspect the question is just designed to check students' ability to cope with linearly shifted data (or coded data as it's often called).
Why did we subtract 50 from 72? The rule doesn’t say that
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old_engineer
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(Original post by Universecolors)
Why did we subtract 50 from 72? The rule doesn’t say that
I didn't design this question, but I suspect that as the original mean score was 51.5, shifting everything down by 50, as opposed to some other number, would be a pragmatic way of limiting the computation of Var(x) to small-ish numbers.
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nerak99
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Well you have to add the 72 into sigma (x-50) where 824>896 and 16 >17.

You then calculate the other parts of the SD formula.

You need to post what you have tried otherwise your post looks like "do my homework".
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Universecolors
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(Original post by nerak99)
Well you have to add the 72 into sigma (x-50) where 824>896 and 16 >17.

You then calculate the other parts of the SD formula.

You need to post what you have tried otherwise your post looks like "do my homework".
What do u mean by adding it into it , i don’t get it , i did do some work , I solved the first part , and I don’t have homework I’m just revising and doing past papers
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Universecolors
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Esme noted the test marks, x, of 16 people in a class. She found that Σ x = 824 and that the standard
deviation of x was 6.5.
(i) CalculateΣ(x−50)andΣ(x−50) ^2. [3](I already did this part )

(ii) One person did the test later and her mark was 72. Calculate the new mean and standard deviation of the marks of all 17 people. [3]


I do not know how to solve part to , for part one you get 24 and 712 respectively

, please help I do not get part 2 , u don’t need to explain the formula , I already know , just got to substitute and organize the numbers
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RDKGames
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No need to have 3 different threads on the same question.

I’ve merged them all.
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CHLO.1
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during sex it started to smell
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Universecolors
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(Original post by RDKGames)
No need to have 3 different threads on the same question.

I’ve merged them all.
Alright
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Universecolors
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(Original post by RDKGames)
No need to have 3 different threads on the same question.

I’ve merged them all.
So do u know how to solve that ?
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RDKGames
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(Original post by Universecolors)
So do u know how to solve that ?
old_engineer has already explained it
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Universecolors
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(Original post by RDKGames)
old_engineer has already explained it
He hasn’t answered my question ? Why do we subtract 72 from 50 ?
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RDKGames
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(Original post by Universecolors)
He hasn’t answered my question ? Why do we subtract 72 from 50 ?
Yes he did but you just seem as if you’re unhappy with his answer...

Every value in the data set has 50 subtracted from them, so you need to subtract 50 from your new piece of data if you are to incorporate it into the rest.
As for why we choose 50, you’d need to ask the actual person who came up with this question because it could’ve been any other number and there’s no actual need for it!
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Universecolors
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(Original post by RDKGames)
Yes he did but you just seem as if you’re unhappy with his answer...

Every value in the data set has 50 subtracted from them, so you need to subtract 50 from your new piece of data if you are to incorporate it into the rest.
As for why we choose 50, you’d need to ask the actual person who came up with this question because it could’ve been any other number and there’s no actual need for it!
Alright then , thank you , I will just try to solve it again
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MarieKane
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(Original post by Universecolors)
I do know the answer and steps for part 1 , I have a problem in part 2 .

Esme noted the test marks, x, of 16 people in a class. She found that Σ x = 824 and that the standard
deviation of x was 6.5.
(i) CalculateΣ(x−50)andΣ(x−50) 2. [3]
(ii) One person did the test later and her mark was 72. Calculate the new mean and standard deviation of the marks of all 17 people. [3]


(i) Σ(x – 50) = 824 – 16 × 50 = 24
Σ(x − 50)^2 =712

ii) (ii) new mean = 896/17 (= 52.7)
712 + 22^2 /17- 24 + (72 − 50) ^2/17
new sd = 7.94


*i do NOT GET why u have to subtract 50 from 72 and can just someone explain the steps for me please , I need help
I think it's because the "new x" is 72
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