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Confidence Interval Examples 1. A recent survey based on 100 TCOB undergraduates showed that 40% of...

Confidence Interval Examples 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? (1) What is the corresponding Z-­‐value? (2) What is the sampling error for the proportion? (3) 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)”. (1) What is the 90% confidence interval for the mean spending? (2) What is the 95% confidence interval for the mean spending? (3) What is the 99% confidence interval for the mean spending?

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Answer #1

A) The 90% confidence interval for the proportion of Iphone users amon TCOB is given by ( 0.3196 , 0.4803 )

B) The 90% confidence interval for mean spending is ( 183.6 , 216.4 )

The 95% confidence interval for the mean spending is ( 180.4 , 219.6)

The 99% confidence interval for the mean spendinf is ( 174.7 , 225.3 )  

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