A manufacturing company produces electrical insulators. If the insulators break when in use, a short circuit is likely to occur. To test the strength of the insulators, destructive testing is carried out to determine how much force is required to break the insulators. Force is measured by observing the number of pounds of force applied to the insulator before it breaks. The following data (stored in force) are from 30 insulators subjected to this testing

1,870 1,728 1,656 1,610 1,634 1,784 1,522 1,696 1,592 1,662
1,866 1,764 1,734 1,662 1,734 1,774 1,550 1,756 1,762 1,866
1,820 1,744 1,788 1,688 1,810 1,752 1,680 1,810 1,652 1,736

a. At the 0.05 level of significance, is there evidence that the population mean force is greater than 1,500 pounds?

b. What assumption about the population distribution is needed in order to conduct the t test in (a)?

c. Construct a histogram, boxplot or normal probability plot to evaluate the assumption made in (b).

d. Do you think that the assumption needed in order to conduct the t test in (a) is valid? explain.