statistics questions

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ajuratli
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a magazine collected data on the total cost of the reception at each of a random sample of 80 weddings. the data is grouped and coded using y=(c-3250)/250 where c is the midpoint in pounds of each class, giving the summary statistics sum of fy= 37 and Syy = 2299.8875using these values, calculate estimates of the mean and standard deviation of the cost of receptions in the sample.please someone help me with this questions
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mqb2766
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(Original post by ajuratli)
a magazine collected data on the total cost of the reception at each of a random sample of 80 weddings. the data is grouped and coded using y=(c-3250)/250 where c is the midpoint in pounds of each class, giving the summary statistics sum of fy= 37 and Syy = 2299.8875using these values, calculate estimates of the mean and standard deviation of the cost of receptions in the sample.please someone help me with this questions
Should be straight forward using the formulas for mean and variance. What are you stuck on?
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ajuratli
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(Original post by mqb2766)
Should be straight forward using the formulas for mean and variance. What are you stuck on?
it's using the code. It came up in the end of topic test and I still don't know how to find 'c'. I got the standard deviation right which was 5.36 but I don't know how to finish it off It's a 7 mark question and I only got 2/7
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mqb2766
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(Original post by ajuratli)
it's using the code. It came up in the end of topic test and I still don't know how to find 'c'. I got the standard deviation right which was 5.36 but I don't know how to finish it off It's a 7 mark question and I only got 2/7
If you have a "linear transformation of a random variable", i.e.
y = mx + c
The mean and standard deviation of the two distributions have a simple relationship
E(y) = E(x) + c
std(y) =m* std(x)
They're reasonably common sense, the c shifts the distribution of x so the mean of y is shifted. The m scales the distribution of x so the standard deviation of y is scaled. Just google the term in quotes to see this.

Try this and post your working?

Edit: note the c in this post is different from your c. The two random variables are x & y and the parameters are m and c.
Last edited by mqb2766; 3 years ago
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