A sample of 50 cotton threads shows the mean breaking strength to be 220 grams and the sample standard deviation to be 12 grams. What is the 95% confidence interval for the standard deviation of breaking strength of the thread.

The confidence interval for this case would be (216.589, 223.411)

Step-by-step explanation:

Information given

represent the sample mean

population mean

s=12 represent the sample standard deviation

n=50 represent the sample size  

Confidence interval

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

  (1)

The degrees of freedom are given by:

The Confidence level is 0.95 or 95%, the significance is and , the critical value for this case is

And replacing we got:

The confidence interval for this case would be (216.589, 223.411)

the equation for this situation is y=122+45. to solve the equation you would add 45 and 122 to get a total of 167lbs. in conclusion, grace's weight eight weeks ago was 167lbs.