Suppose that one in six smartphone users have fallen prey to cyber-attack. We use a sample of 155 smartphone users. a-1. What is the expected value and the standard error of the sample proportion? (Round "Expected value" to 2 decimal places and "Standard error" to 4 decimal places.) a-2. Is it appropriate to use the normal distribution approximation for the sample proportion? multiple choice

• Yes, because np 5 and n(1 - p) 5
• Yes, because n 30
• No, because np 5 and n(1 - p) 5
• No, because n < 30

b. What is the probability that more than 21% of smartphone users in the sample have fallen prey to cyber-attack? (Round final answer to 2 decimal places.)