Given Information: Number of defective cups = 15 Total number of cups = 300 Required Information: a) defective proportion = p = ? B) 95% confidence interval of defective proportion = ? a) defective proportion = p = 0.05 = 5% b) 95% confidence interval of defective proportion = (2.5%, 7.5%) Step-by-step explanation: The estimated defective proportion is given by p = Number of defective cups/Total number of cups p = 15/300 p = 0.05 p = 5% The confidence interval of defective proportion is given by Where p is the defective proportion, z is the z-score corresponding to 95% confidence level and n is the total number of cups. The z-score corresponding to 95% confidence level is 1.96 CI = (2.5%, 7.5%) So that means we are 95% confident that the defective proportion is between 2.5% to 7.5%. Zack should not return this lot since the defective percentage is below 10%