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# S2 Hypothesis testing watch

1. Need help with 13c.

For an alternative conclusion it would mean we would reject Ho, so our z value would be less than -1.645?

Not sure how you work out the sum of x^2 though.
Thanks

hmm that is a bit ****, it doesn't allow me to upload the photo? Anyone know how to fix that problem?

I think this should work: http://i64.tinypic.com/2ppc9ap.jpg
2. (Original post by Super199)
Need help with 13c.

For an alternative conclusion it would mean we would reject Ho, so our z value would be less than -1.645?

Not sure how you work out the sum of x^2 though.
Thanks

hmm that is a bit ****, it doesn't allow me to upload the photo? Anyone know how to fix that problem?
How are you trying to upload it?

What message do you get?
3. (Original post by SeanFM)
How are you trying to upload it?

What message do you get?
The attachments thing and it comes up with a server error.
4. (Original post by Super199)
The attachments thing and it comes up with a server error.
Maybe try insert image if possible?
5. (Original post by SeanFM)
Maybe try insert image if possible?
Doesn't work either. :/
6. (Original post by Super199)
Doesn't work either. :/

Hm.. it may be worth typing it out?

Or finding the same question online somewhere if possible.
Attached Images

7. (Original post by Super199)
Need help with 13c.

For an alternative conclusion it would mean we would reject Ho, so our z value would be less than -1.645?

Not sure how you work out the sum of x^2 though.
Thanks

hmm that is a bit ****, it doesn't allow me to upload the photo? Anyone know how to fix that problem?
8. (Original post by SeanFM)

Hm.. it may be worth typing it out?

Or finding the same question online somewhere if possible.
http://i64.tinypic.com/2ppc9ap.jpg

btw where was that photo taken?
9. (Original post by Super199)
http://i64.tinypic.com/2ppc9ap.jpg

btw where was that photo taken?
University of Bath campus, by the lake

I think that what you said about the z value is correct - and we can assume that the sum of x (and so the sample mean are correct), so the thing that we're in interested in is theta/n, which depends on the sum of x^2...
10. (Original post by SeanFM)
University of Bath campus, by the lake

I think that what you said about the z value is correct - and we can assume that the sum of x (and so the sample mean are correct), so the thing that we're in interested in is theta/n, which depends on the sum of x^2...
theta/n?
11. (Original post by Super199)
theta/n?
Sorry, I got sigma and theta mixed up (I'm doing stats work involving theta, sorry! )

The only unknown is sigma (the standard deviation) which depends on the variance, which depends on the sum of x^2.. so can you see how to find the 'correct' value of sigma?
12. (Original post by SeanFM)
Sorry, I got sigma and theta mixed up (I'm doing stats work involving theta, sorry! )

The only unknown is sigma (the standard deviation) which depends on the variance, which depends on the sum of x^2.. so can you see how to find the 'correct' value of sigma?
Not really.
What I have done is put the standard deviation = sum of x^2/n - mean^2

Thought the standard deviation would be the square root of my sample variance and then tried rearranging for sum of x^2
13. (Original post by Super199)
Not really.
What I have done is put the standard deviation = sum of x^2/n - mean^2

Thought the standard deviation would be the square root of my sample variance and then tried rearranging for sum of x^2
Yes, that's correct... now the only thing you're missing is the standard deviation.
14. (Original post by SeanFM)
Yes, that's correct... now the only thing you're missing is the standard deviation.
Yeah but what is the standard deviation?
I used the equation and got 82.7?
15. (Original post by Super199)
Yeah but what is the standard deviation?
It's to do with the value for which the hypothesis is rejected.
16. (Original post by SeanFM)
It's to do with the value for which the hypothesis is rejected.
Nah idek anymore i give up haha
17. (Original post by Super199)
Nah idek anymore i give up haha
From what I understand, the sample mean is fixed, the mean that you're testing (30) is fixed, and the z value that you need to get from the test to get a different conclusion (which you've already identified) so you need to find the value of the standard deviation that satisfies that equation, and then you can use the formula you've just defined (for the sum of x^2).
18. (Original post by SeanFM)
From what I understand, the sample mean is fixed, the mean that you're testing (30) is fixed, and the z value that you need to get from the test to get a different conclusion (which you've already identified) so you need to find the value of the standard deviation that satisfies that equation, and then you can use the formula you've just defined (for the sum of x^2).
For the rejection of Ho. It would have to be -1.646>-1.645?

You may need to give me a full solution. I would try and post my working but attachments dont seem to work .
19. (Original post by Super199)
For the rejection of Ho. It would have to be -1.646>-1.645?

You may need to give me a full solution. I would try and post my working but attachments dont seem to work .
I seem to be getting 106665 which is out by a bit, so perhaps the method is wrong.
Spoiler:
Show
z must be less than -1.6449, so , and we know what xbar, mu and n are so we find that (28.9-30)/-1.6449 = sigma/sqrt(120), so rearrange to find sigma, square that, then use the formula for add (sample mean)^2 and multiply by n... to get the wrong answer.
20. (Original post by SeanFM)
I seem to be getting 106665 which is out by a bit, so perhaps the method is wrong.
Spoiler:
Show
z must be less than -1.6449, so , and we know what xbar, mu and n are so we find that (28.9-30)/-1.6449 = sigma/sqrt(120), so rearrange to find sigma, square that, then use the formula for add (sample mean)^2 and multiply by n... to get the wrong answer.
Whats the reason for using -1.6449?

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