In: Statistics and Probability
The US Navy is interested in acquiring a new communications relay for its submarines. Manufacturers tested 50 units and found the mean time between failures to be 2607 minutes, and the sample standard deviation to be 675. Find a 95% CI for the mean time between failures. (Assume the sample comes from a normal population.)
Solution :
Given that,
= 2607
s = 675
n = 50
Degrees of freedom = df = n - 1 = 50 - 1 = 49
At 95% confidence level the t is ,
= 1 - 95% = 1 - 0.95 = 0.05
/ 2 = 0.05 / 2 = 0.025
t /2,df = t0.025,49 = 2.010
Margin of error = E = t/2,df * (s /n)
= 2.010 * (675 / 50)
= 191.87
Margin of error = 191.87
The 95% confidence interval estimate of the population mean is,
- E < < + E
2607 - 191.87 < < 2607 + 191.87
2415.13 < < 2798.87
( 2415.13, 2798.87 )