A control chart for nonconformities is to be established in conjunction with the final inspection of a

Question:

A control chart for nonconformities is to be established in conjunction with the final inspection of a radio. The inspection unit is to be a group of ten radios. The average number of nonconformities per radio has, in the past, been 0.5. Find three-sigma control limits for a c chart based on this size of inspection unit.