Question

A manufacturing company produces electric insulators. You define the variable of interest as the strength of the insulators. If the insulators break when in​ use, a short circuit is likely. To test the strength of the​ insulators, you carry out destructive testing to determine how much force is required to break the insulators. You measure force by observing how many pounds are applied to the insulator before it breaks. The accompanying data represent the amount of force required to break a sample of 30.

a. Construct a 90% confidence interval for the population mean force.

1,855

1,672

1,571

1,728

1,699

1,631

1,628

1,783

1,560

1,672

1,858

1,693

1,714

1,664

1,716

1,770

1,743

1,758

1,783

1,886

1,807

1,719

1,759

1,661

1,845

1,753

1,663

1,824

1,695

1,701

Answer 1

The 90% confidence interval for mean is given as .

The descriptives of the given data is as follows.

Now substitute the respective statistic measures in the interval.

   (the critical value is 1.699 as from the t-table for 29 degrees of freedom and 5% level)

The 90% confidence interval for the population mean force of the insulators is (1701.71, 1752.36)