Answer
12 < $\mu$ < 12.6
Work Step by Step
c =0.90, $\bar{x}$ = 12.3, $\sigma$ = 1.5, n =50
Formula for CI:
$\bar{x}$ $\pm$ ( z$\times$$\frac{\sigma}{\sqrt n}$)
1) The z score that corresponds to a 90% confidence level is 1.645
2) Find the margin of error
1.645 x $\frac{1.5}{\sqrt 50}$ $\approx$ 0.349
3) Find the bounds of the interval
12.3 - 0.349 = 11.951
12.3 + 0.349 = 12.649
Therefore the Confidence interval is
11.951 < $\mu$ < 12.649
$\approx$ 12 < $\mu$ < 12.6
