Question

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?

Answer #1

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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