In: Statistics and Probability
. Construct a 98% confidence interval for the average monthly apartment rent using a random sample of 32 apartments with a mean of $375 and a standard deviation of 32.5.
Solution :
Given that,
Point estimate = sample mean = 
 = $375
Population standard deviation =   
= $32.5
Sample size = n =32
At 98% confidence level the z is ,
= 1 - 98% = 1 - 0.98 = 0.02
/ 2 = 0.02/ 2 = 0.01
Z
/2
= Z0.01 = 2.326 ( Using z table    )
Margin of error = E = Z
/2
* ( 
 /n)
= 2.326 * ( 32.5 /  32
)
E= 13.3634
At 98% confidence interval estimate of the population mean
is,
- E < 
 < 
 + E
375 - 13.3634 <  
< 375 + 13.3634
361.6366<  
< 388.3634
( 361.6366, 388.3634 )