Recall the formula for the margin of error, E, given below where zw/2 is the z value corresponding to an upper tail area of 2 and a confidence level of 1 - 4,p is the point estimati population proportion, and n is the sample size. E=z/2n(1p) There were 1,007 adults in the survey, so n= X, and the sample proportion was found to be p=0.57. Now the value of zw/ is needed. A margin of error for 90% confidence is needed. Common values for za2 for various confidence levels are given below. According to the table, for a 90% confidence level, the necessary value for za/2 is