Market research A marketing researcher for a phone company surveys 100 people and finds that the proportion of customers who are likely to switch providers when their contract expires is 15%.  a) What...

Market research A marketing researcher for a phone company surveys 100 people and finds that the proportion of customers who are likely to switch providers when their contract expires is 15%.

 a) What is the standard deviation of the sampling distribution of the proportion?

 b) If she wants to reduce the standard deviation by half, how large a sample would she need?