Question

A survey of 495 citizens found that 342 of them favor a new bill introduced by the city. We want to find a 95% confidence interval for the true proportion of the population who favor the bill. What is the lower limit of the interval? Use the 68-95-99.7% rule our use the Z table. How do I do this in excel?

Answer 1

x	342
n	495
p-hat(x/n)	0.690909091
SE= sqrt(p-hat(1-p-hat)/n)	0.020770692
Z=NORMSINV(1-0.025)	1.959963985
E(margin of error)=Z*SE	0.040709809

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	Lower Limit	Upper Limit
95% CI	(p-hat)-E	(p-hat)+E
Answer	0.650199282	0.7316189

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Lower Limit of the Interval = 0.650199282

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Note - Round down decimal places according to your requirement