In: Statistics and Probability
Survey of 85 company employees shows that the mean length of the Christmas vacation was 4.5 days, with a standard deviation of 1.2 days. Construct a 92% confidence interval for the population mean length of vacation [5 points]. Interpret the results using complete sentences. [5 points]
Solution :
Given that,
Point estimate = sample mean =  
   = 4.5
Population standard deviation =   
= 1.2
Sample size n =85
At 92% confidence level the z is ,
Z
/2
= Z0.04 = 1.75   ( Using z table )
Margin of error = E =   Z
/2   
* ( 
 /n)
= 1.75 * ( 1.2 / 85)
E= 0.2278
At 92% confidence interval estimate of the population mean
is,
- E < 
 < 
 + E
4.5 - 0.2278 <  
<4.5 + 0.2278
4.2722 <  
< 4.7278
( 4.2722 , 4.7278 )