According to a recent FCC survey, one in four cell phone users has experienced bill shock from unexpectedly high cell phone bills. A sample of 200 cell phone users was collected 1. what is the probability that more than 20% of cell phone users in the sample have experienced bill shock? a. b. What is the standard error of the proportion? An economist reports that 576 out of a sample of 1,200 middle-income American households participate in the stock market. A confidence interval of [0.468, 0.492] was calculated. confidence level was used in this calculation?