# Statistics 3 helpWatch

Thread starter 2 years ago
#1
Q1. A garage sells both leaded and unleaded pertrol. The distribution of the values of sales for each type is normal. During the 1990 the standard deviation of individual sales of each type of petrol is \$3.25. The mean of the individual sales of leaded petrol during this time is \$8.72. A random sample of 100 individual sales of unleaded petrol gave a mean of \$9.71. Calculate:

c. an interval within which 90% of the sales of leaded petrol will lie

Population mean is 8.72, sd is 3.25 but whats n for leaded?

Q2. A machine fills 1kg packets of sugar. The actual weight of sugar delivered to each packet can be assumed to be normally distributed. The manufacturer requires that, the mean weight of the contents of a packet is 1010g and 95% of all packets filled by the machine contains between 1000g and 1020g of sugar.

a. Show that this is equivalent to demanding that the variance of the sampling distribution to 2dp is equal to 26.03g.

Here if I use the width - confidence level formula I get the value n which is unknown. I know they ask for a packet so n=1? and the answer is right but im not sure if its the correct way..

*Deleted Q3 as i can do it now
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2 years ago
#2
In the first two questions, you are talking about the actual values from the distributions, not the means of samples. As you suggest in Q2, this is mathematically equivalent to taking samples of size 1, but it's more in tune with the problem to use the original distribution rather than thinking of samples at all.
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Thread starter 2 years ago
#3
(Original post by Pangol)
In the first two questions, you are talking about the actual values from the distributions, not the means of samples. As you suggest in Q2, this is mathematically equivalent to taking samples of size 1, but it's more in tune with the problem to use the original distribution rather than thinking of samples at all.
For questions 1 and 2 i was taken into consideration the population means not sample means. The formula for working out the confidence intervals is same if you have population mean or sample mean isnt it? Same for question 2
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Thread starter 2 years ago
#4
Kevin De Bruyne, ghostwalker

Can someone help me with Q1 and 2, cant move on to doing exam q's before i get through this,thanks
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