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# Hypothesis Testing Watch

1. Prior to servicing, the length of bolts made by a machine followed a normal distribution with mean length 8.59 and standard deviation 0.39.

After servicing, a random sample of 20 bolts were measured. It was found they had a sample mean of 7.51 and a sample variance of 0.66.

What is the test statistic of the null hypothesis that the servicing has not affected the mean length of bolts produce by the machine, if it is known that it has not affected the variance?
2. I havent done much normal hypothesis testing (only just started S3) so I'm not too sure. Will post back if I have ideas
3. just remembered you have to use the test statistic: z=(X(bar)-mu)/(sigma/sqrt(n)). Where n is the number of the sample taken. This relies on the Central Limit Theorem i.e. that the means are normally distributed.

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