Question

A
random Sample of 79 light bulbs had a mean Iife of 400 hours with
standard deviation of 28 hours. Construct 90% interval for the mean
life of light bulbs

Answer #1

Solution :

Given that,

Point estimate = sample mean = = 400

sample standard deviation = s = 28

sample size = n = 79

Degrees of freedom = df = n - 1 = 78

At 90% confidence level the t is ,

t_{
/2,df} = t_{0.05,78} = 1.665

Margin of error = E = t_{/2,df}
* (s /n)

= 1.665 * (28 / 79)

= 5.245

The 95% confidence interval estimate of the population mean is,

- E < < + E

400 - 5.245 < < 400 + 5.245

394.755 < < 405.245

(394.755 , 405.245)

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