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# S1 - confidence intervals, HELP! Watch

1. So, i'm stuck on part B of this question;

Rice that can be cooked in microwave ovens is sold in packets which the manufacturer claims contain a mean weight of more than 250 grams of rice.

The weight of rice in a packet may be modelled by a normal distribution.

A consumer organisation’s researcher weighed the contents, x grams, of each of a random sample of 50 packets. Her summarised results are:

and

(a) Show that, correct to two decimal places, , where denotes the unbiased estimate of the population variance.

(b) Construct a 96% confidence interval for the mean weight of rice in a packet, giving the limits to one decimal place.

And i've looked at the mark scheme and it says that i should be using 0.98 instead of 0.96 but i don't understand why, it says 96% confidence interval. I'm sure i'm just being an idiot, but can someone help? please?
2. (Original post by Jasprar)
And i've looked at the mark scheme and it says that i should be using 0.98 instead of 0.96 but i don't understand why, it says 96% confidence interval. I'm sure i'm just being an idiot, but can someone help? please?
96% means 4% in the tails, i.e 2% in each tail. So you need the z value for 0.98.
3. (Original post by ghostwalker)
96% means 4% in the tails, i.e 2% in each tail. So you need the z value for 0.98.
Surely you'd need the z value for a central 0.96 not 0.98? If its 96% you want the central 0.96. Hmmmm...

Which paper is it?

Anyways...

Then use the formula X bar plus minus Z multiplied by (s divided by the root of n)

Sorry for the use of words, don't know latex :')
4. (Original post by Dingo749)
Surely you'd need the z value for a central 0.96 not 0.98? If its 96% you want the central 0.96. Hmmmm...
Central 0.96, implies looking at the cumulative value of 0.98 for a 2-tailed test.

Which paper is it?
No idea - ask the OP.
5. u guys ready for s1?
6. Is the answer [250.5, 251.7] ??

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