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.

A binomial experiment is given. Determine whether you can use a normal distribution to approximate the binomial distribution. If you can, find the mean and standard deviation. If you cannot, explain why.