You intend to estimate a population mean $\displaystyle \mu$ with the following sample.

49.4
51.9
34.2
-12.9
20.9
30.2
16.7
-26.7
-20.8
8.2
4.9
28.8

You believe the population is normally distributed. Find the 90% confidence interval. Enter your answer as an open-interval (i.e., parentheses) accurate to twp decimal places (because the sample data are reported accurate to one decimal place).

90% C.I. =

Answer should be obtained without any preliminary rounding. However, the critical value may be rounded to 3 decimal places.