In: Statistics and Probability
The table below contains the overall miles per gallon (MPG) of a type of vehicle. Complete parts a and b below.
| 
 2929  | 
 2727  | 
 2323  | 
 3535  | 
 2828  | 
 2020  | 
 2828  | 
 3030  | 
 2929  | 
 2727  | 
 3535  | 
 2929  | 
 3434  | 
 3333  | 
a. Construct a 99% confidence interval estimate for the population mean MPG for this type of vehicle, assuming a normal distribution. The 99% confidence interval estimate is from:
MPG to MPG.
(Round to one decimal place as needed.)
b. Interpret the interval constructed in (a)
Solution:
| x | x2 | 
| 2929 | 8579041 | 
| 2727 | 7436529 | 
| 2323 | 5396329 | 
| 3535 | 12496225 | 
| 2828 | 7997584 | 
| 2020 | 4080400 | 
| 2828 | 7997584 | 
| 3030 | 9180900 | 
| 2929 | 8579041 | 
| 2273 | 5166529 | 
| 5352 | 28643904 | 
| 9293 | 86359849 | 
| 4343 | 18861649 | 
| 3333 | 11108889 | 
 x
= 49753 | 
 x2
= 221884453 | 
a ) The sample mean is 
Mean 
  = (
x
/ n) )
= ( 2929 + 2727 + 2323 + 3535 + 2828 + 2020 + 2828 + 3030 + 2929 + 2727 + 3535 + 2929 + 3434 + 3333 / 14 )
= 49753/ 14
= 3553.0714
Mean 
  = 3553.1
The sample standard is S
  S = 
 ( 
 x2 ) - (( 
x)2 / n ) n -1
= 
 (221884453 ( 49753 )2 / 14 ) 13
   = 
( 221884453 - 176740432.0714 / 13)
=
(45144020.9286 / 913)
= 
3472616.9945
= 1863.4959
The sample standard is 1863.5
b ) At 99% confidence level the t is ,
= 1 - 99% = 1 - 0.99 = 0.01
/ 2 = 0.01 / 2 = 0.005
t
/2,df = t0.005,13 = 3.012
Margin of error = E = t
/2,df
* (s /n)
= 3.012 * (1863.5 / 
14)
= 1500.1
Margin of error = 1500.1
The 99% confidence interval estimate of the population mean is,
- E < 
 < 
 + E
3553.1 - 1500.1 < 
 < 3553.1 + 1500.1
20523.0< 
 < 5053.2
(20523.0, 5053.2 )