A random sample of 20 purchases showed the amounts in the table (in $). The mean is $49.33 and the standard deviation is $20.88.
| 42.14 |
82.47 |
74.40 |
| 42.16 |
7.39 |
56.92 |
| 62.28 |
26.41 |
38.59 |
| 62.93 |
48.78 |
59.05 |
| 23.72 |
51.76 |
39.33 |
| 43.73 |
86.76 |
39.65 |
| 24.03 |
74.18 |
|
A) Construct a 80% confidence interval for the mean purchases of all customers, assuming that assumptions and coditions for cofidence interval have been met. (What is the confidence interval)?
B) What is the margin of error?
C) How would the confidence interval change if you had assumed that the standard deviation was known to be $21 ? (Basically, what is the confidence interval using the given purchases standard deviation)?