Acme Corporation manufactures light bulbs rated to last 300
days. A sample of 20 bulbs are tested and last an average of 290
days, with a standard deviation of 50 days. Given this data,
construct a 80% confidence interval for the mean.
What is the value of t from the table?
What is the confidence interval?
Solution :
Given that,
t /2,df = 1.328
Margin of error = E = t/2,df * (s /n)
= 1.328 * (50 / 20)
= 14.8
The 80% confidence interval estimate of the population mean is,
- E < < + E
290 - 14.8 < < 290 + 14.8
275.2 < < 304.8
The confidence interval is (275.2 , 304.8)
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