Question
The king of a large castle would like to estimate the average age of knights currently...
The king of a large castle would like to estimate the average age of knights currently enrolled. Previous studies show a standard deviation of 2 years in knight ages.
a. If in a random sample of 25 knights at the castle, the average age x was found to be 23.2 years old, find a 95% confidence interval for the average age of all knights at the castle.
b. If the king wanted a 95% confidence interval for the average knight age that was no more than 1 year in width, how large a sample of knights would be needed?
Homework Answers
Answer #1
a)
95% Confidence Interval :-
X̅ ± Z( α /2) σ / √ ( n )
Z(α/2) = Z (0.05 /2) = 1.96
23.2 ± Z (0.05/2 ) * 2/√(25)
Lower Limit = 23.2 - Z(0.05/2) 2/√(25)
Lower Limit = 22.416
Upper Limit = 23.2 + Z(0.05/2) 2/√(25)
Upper Limit = 23.984
95% Confidence interval is ( 22.416 , 23.984
)
b)
Margin of error E = Width of confidence interval / 2 = 1 / 2 = 0.5
Sample size = (Z
/2
* 
/ E)2
= ( 1.96 * 2 / 0.5)2
= 61.5
Sample size = 62 (Rounded up to nearest integer)
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