Answer
See below
Work Step by Step
Formula for CI
$\bar{x}$ $\pm$ ( z$\times$$\frac{\sigma}{\sqrt n}$)
i) $23 \pm ( 1.645\times\frac{6.7}{\sqrt 36})$
= $23\pm 1.8369$
CI: $21.1631 < \mu < 24.8369 \approx 21.2 < \mu < 24.8$
Interpretation: With 90% confidence, it can be said that the population mean sodium chloride concentration lies between 21.2 cubic centimeters and 24.8 cubic centimeters
ii) i) $23 \pm ( 1.96\times\frac{6.7}{\sqrt 36}$)
= $23 \pm 2.189$
CI: $20.811 < \mu < 25.189 \approx 20.8 < \mu < 25.2$
Interpretation: With 95% confidence, it can be said that the population mean sodium chloride concentration lies between 20.8 cubic centimeters and 25.2 cubic centimeters
iii) The 95% CI is wider
