Posted by sam on Saturday, April 21, 2012 at 6:02pm.
A random sample of n=500 households in a certain metropolitan area revealed that 150 have combined cable, phone and internet service.
a.Calculate phat, the sample proportion of households having such service.
b.Calculate a confidence interval for π, the proportion of all households in this area that have such service; use a confidence level of 90%.

Stats  MathGuru, Saturday, April 21, 2012 at 7:09pm
For a): phat = x/n = 150/500 (convert to a decimal to use in part b).
For b): CI90 = p ± (1.645)[√(pq/n)]
...where p = x/n, q = 1  p, and n = sample size.
Note: ± 1.645 represents 90% confidence interval.
Hopefully, you can take it from here.
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