A research group wants to estimate the percent of consumers who plan to buy a new cell phone in the next three month. What is the required sample size for a sampling error no more than .04 and a confidence level of 95%?

Many Americans work at home or in the weekends in addition to their work hours. If you want to estimate the mean weekend work hours with a 5 minutes margin of error, how many workers would you sample? Assume sigma=10 minutes. Use a .10 significance level (90% confidence)