Question

A random sample of 85 group leaders, supervisors and similar personnel at General Motors revealed that, on average, they spent 6.5 years in a particular job before being promoted. The standard deviation of the sample was 1.7 years. Construct a 95% confidence interval.  

• Explain which words in the problem indicate a z-distribution or a t-distribution (choose one).
• Show how to calculate the confidence interval using Excel or typing out the equation (such as for proportions). The purpose is to identify a correct equation (with numbers typed out for all to learn) to solve these problems. Note: You must pick your own problem for this post that has not yet been used by another student. Put the problem number you chose in the title of your post.

Answer 1

In above problem , sample size is 85. When sample size is 30 or less than 30 we use t distributind and when sample size is greter than 30 we use z distribution.

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