In: Statistics and Probability
1. A sample of 48 aircraft “C” checks generated an average of 238 write-ups (squawks), with a standard deviation of 39. The VP of operations wants to know how many squawks to expect on the next “C” check performed. Can you give him an estimate based on a 95% degree of confidence?
Solution :
Given that,
Point estimate = sample mean =
= 238
Population standard deviation =
= 39
Sample size = n =48
At 95% confidence level the z is ,
= 1 - 95% = 1 - 0.95 = 0.05
/ 2 = 0.05 / 2 = 0.025
Z/2 = Z0.025 = 1.96
Margin of error = E = Z/2
* (
/n)
= 1.96 * (39 / 48
)
= 11.0332
At 95% confidence interval estimate of the population mean
is,
- E <
<
+ E
238 -11.0332 <
< 238+ 11.0332
226.9668 <
< 249.0332
( 226.9668 , 249.0332 )