Question

From 19 measurements of a pressure controller, the mean operating pressure is 4.97 kPa with a standard deviation of 0.0461 kPa. Neglecting other sources or error, state the population true mean pressure at 95% confidence.

Answer 1

Answer:

   

   

So on this case the 95% confidence interval would be given by (4.95;4.99)  

Step-by-step explanation:

Previous concepts

A confidence interval is "a range of values that’s likely to include a population value with a certain degree of confidence. It is often expressed a % whereby a population means lies between an upper and lower interval".

The margin of error is the range of values below and above the sample statistic in a confidence interval.

Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".

represent the sample mean

population mean (variable of interest)

s=0.0461 represent the sample standard deviation

n=19 represent the sample size  

Confidence interval

The confidence interval for the mean is given by the following formula:

  (1)

In order to calculate the critical value  we need to find first the degrees of freedom, given by:

Since the Confidence is 0.95 or 95%, the value of  and , and we can use excel, a calculator or a table to find the critical value. The excel command would be: "=-T.INV(0.025,18)".And we see that  

Now we have everything in order to replace into formula (1):

   

   

So on this case the 95% confidence interval would be given by (4.95;4.99)