Answer
144.80 < $\mu$ < 155.20
Work Step by Step
Formula for CI:
$\bar{x}$ $\pm$ ( z$\times$$\frac{\sigma}{\sqrt n}$)
= $150 \pm ( 2.5758\times\frac{15.50}{\sqrt60 })$
= $150\pm 5.154$
CI: $144.8461 < \mu < 155.154 \approx 144.80 < \mu < 155.20$
Interpretation: With 99% confidence, it can be said that the population mean repair cost lies between \$144.80 and \$155.20
