Amanufacturer of a certain type of large ma- chine wishes to buy rivets from one of two manufac- turers. it is important that the breaking strength of each rivet exceed 10,000 psi. two manufacturers (a and b) offer this type of rivet and both have rivets whose breaking strength is normally distributed. the mean breaking strengths for manufacturers a and b are 14,000 psi and 13,000 psi, respectively. the stan- dard deviations are 2000 psi and 1000 psi, respectively. which manufacturer will produce, on the average, the fewest number of defective rivets?