The lifetime of a new stereo is estimated to be 12 years with a standard deviation of 2.5 years.
A. What is the probability of the stereo failing after 4 years?
B. If there is a full replacement guarantee of 3.5 years, What is the expected proportion of replacements?
C. If the firm is willing to replace up to 3%, What guarantee period should it specify?
Please show your work