In: Statistics and Probability
The owner of a trout farm routinely measures the lengths of his trouts. He randomly took 31 trouts last Friday from his pond and measured their lengths. The mean length was 26.1 centimeters with a standard deviation of 1.8. Estimate the true mean length of all trouts in his farm using a 90% confidence interval.
(a) The limits of the confidence interval are calculated by x¯±tsn‾√x¯±tsn , where
x¯=
t= (Round to 3 decimal places.) Please explain how to find this!
s=
n=
(b) The 90% confidence interval for the true mean length is: ( , ) (Round to 3 decimal places.)
Solution :
Given that,
= 26.1
s = 1.8
n = 25
Degrees of freedom = df = n - 1 = 31 - 1 = 30
At 90% confidence level the z is ,
= 1 - 90% = 1 - 0.90 = 0.10
/ 2 = 0.10 / 2 = 0.05
t /2,df = t0.05,30 = 1.697
Margin of error = E = t/2,df * (s /n)
= 1.697 * ( 1.8 / 31)
= 0.549
Margin of error = 0.549
The 90% confidence interval estimate of the population mean is,
- E < < + E
26.1 - 0.549 < < 26.1 + 0.549
25.551 < < 26.649
(25.551, 26.649 )