In: Statistics and Probability
Develop a 90% confidence interval for the household income of subscribers. DATA
| Household Income ($) |
| 58600 |
| 54200 |
| 38500 |
| 148600 |
| 82100 |
| 64400 |
| 86200 |
| 177100 |
| 68300 |
| 67900 |
| 57300 |
| 83600 |
| 77500 |
| 68200 |
| 61900 |
| 57600 |
| 82300 |
| 64600 |
| 61100 |
| 31200 |
| 92600 |
| 68300 |
| 35100 |
| 85700 |
| 140300 |
| 108200 |
| 61100 |
| 33900 |
| 54400 |
| 61200 |
| 58000 |
| 90700 |
| 95200 |
| 50500 |
| 33800 |
| 147400 |
| 92600 |
| 66200 |
| 45700 |
| 60500 |
| 110600 |
| 60300 |
| 75700 |
| 70100 |
| 42100 |
| 41700 |
| 96900 |
| 65700 |
| 50200 |
| 61700 |
| 44500 |
| 51900 |
| 119100 |
| 49200 |
| 39000 |
| 35000 |
| 104700 |
| 49300 |
| 74000 |
| 57100 |
| 51400 |
| 62100 |
| 103000 |
| 97900 |
| 123100 |
| 322500 |
| 54800 |
| 66500 |
| 33700 |
| 73600 |
| 71300 |
| 74200 |
| 70000 |
| 40800 |
| 72500 |
| 53300 |
| 45600 |
| 73900 |
| 83600 |
| 124700 |
| 101600 |
| 205900 |
| 69700 |
| 95700 |
| 46100 |
| 118600 |
| 65400 |
| 149300 |
| 125000 |
| 39800 |
| 83500 |
| 38700 |
| 102400 |
| 57700 |
| 16200 |
| 43100 |
| 43700 |
| 39600 |
| 127500 |
| 33500 |
| 48100 |
| 52800 |
| 54800 |
| 46500 |
| 60400 |
From the given data the following were calculated
| n | 105 |
| Sum | 7835500 |
| Average | 74623.810 |
| SS(Sum of squares) | 1.74735E* 1011 |
| Variance = SS/n-1 | 1680141254.579 |
| Std Dev=Sqrt(Variance) | 40989.5262 |
_________________________________________________________________
sample mean (
)
= 74623.81, Standard Deviation (s) = 40989.526, n = 105
The Zcritical at
= 0.10 = 1.645
Although population standard deviation is not known, n is large and we can assume Z critical values
The Confidence Interval is given by
ME, where

The Lower Limit = 74623.810 - 6580.287 = 68043.533
The Upper Limit = 74623.810 + 6580.287 = 81204.087
The Confidence Interval is (68043.533 , 81204.087)
_____________________________________________________
If required to 2 decimal places. then the 90% CI is (68043.53, 81204.09)
If required to 1 decimal places. then the 90% CI is (68043.5, 81204.1)
If required to the nearest dollar. then the 90% CI is (68044, 81204)