Continuing with the ECCO company from Exercise 4-83, when a customer returns one of the alarms under warranty, the quality manager logs data on the product. From the data available in the Ecco file, use relative frequency to answer these questions.

a. If a part was made in the Salt Lake City plant, what is the probability the cause of the returned part was wiring?

b. If the company incurs a $30 cost for each returned alarm, what percentage of the cost should be assigned to each plant if it is known that 70% of all production is done in Boise, 20% in Salt Lake City, and the rest in Toronto?