1.A recent survey based on 100 TCOB undergraduates showed that 40% of the respondents were using an Iphone. What is the 90% confidence interval for the proportion of Iphone users among TCOB undergraduates?

a. What is the corresponding Z-value?

b. What is the sampling error for the proportion?

c. What is the confidence interval?

2.A sample study of 100 customers of Best Buy showed that the average dollar spending during the last three months was 200 dollars with the sample standard deviation of 100. A manager wants to know "what is the average spending of its customers (population, not the sample)".

a. What is the 90% confidence interval for the mean spending?

b. What is the 95% confidence interval for the mean spending?

c. What is the 99% confidence interval for the mean spending?