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S3 Confidence intervals

This seems a stupid question but why does it equal to 6.86 and not 5?
I know 5 would just give me 1.96 again but I dont understand the 6.86s3 q13.png
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Zacken
22
Original post by RK1998
This seems a stupid question but why does it equal to 6.86 and not 5?
I know 5 would just give me 1.96 again but I dont understand the 6.86s3 q13.png



141.86−128.142=6.86\displaystyle \frac{141.86 - 128.14}{2} = 6.86.
Reply 2
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RK1998
OP
5
Original post by Zacken
141.86−128.142=6.86\displaystyle \frac{141.86 - 128.14}{2} = 6.86.


So it's just the difference of the intervals divided by 2.
Thank you so much :smile:

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Reply 3
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Zacken
22
Original post by RK1998
So it's just the difference of the intervals divided by 2.
Thank you so much :smile:


Yes, you know the width of an interval is given by 2×z×σn2 \times z \times \frac{\sigma}{\sqrt{n}} but the width here is the difference of the limits.

So 2×z×σn=13.722 \times z \times \frac{\sigma}{\sqrt{n}} = 13.72 and then dividing both sides by 2 gets you your answer.

You're very welcome.

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