In LCD screens, every attempt is made to make sure that all pixels illuminate when they receive a signal, but it is impossible to ensure that every pixel in a large screen will actually work. A screen is determined to be defective if more than 2 pixels fail to light. Every week 500 screens are randomly selected and a quality control team member counts the number of defective screens. Out of 500 screens, management would like an average of no more than 5 defective screens. The results for the last 50 weeks are shown in the following table.
a) Create a c chart.
b) Is the number of defective screens out of control? Comment.