The defect length of a corrosion defect in a pressurized steel pipe is normally distributed with mean value 31 mm and standard deviation 7 7 mm USE SALT a What is the probability that defect length is at most 20 mm Less than 20 mm Round your answers to four decimal places at most 20mm less than 20mm b What is the 75th percentile of the defect length distribution that is the value that separates the smallest 75 of all lengths from the largest 25 Round your answer to four decimal place mm c What is the 15th percentile of the defect length distribution Round your answer to four decimal places mm d What values separate the middle 80 of the defect length distribution from the smallest 10 and the largest 10 Round your answers to four decimal places smallest 10 largest 10 mm mm