Chapter 5.5, Problem 21E

Approximating Binomial Probabilities In Exercises 19-26, determine whether you can use a normal distribution to approximate the binomial distribution. If you can, use the normal distribution to approximate the indicated probabilities and sketch their graphs. If you cannot, explain why and use a binomial distribution to find the indicated probabilities. Identify any unusual events. Explain.

21. Screen Lock A survey of U.S. adults found that 28% of those who own smartphones do not use a screen lock or other security features to access their phone. You randomly select 150 U.S. adults who own smartphones. Find the probability that the number who do not use a screen lock or other security features to access their phone is (a) at most 40, (b) more than 50, and (c) between 20 and 30, inclusive. (Source: Pew Research Center)