To determine whether the null hypothesis \( H_{0}: \mu = 2 \) can be rejected at the 0.05 level, we look at the 95% confidence interval for \(\mu\), which is given as (1.55, 4.20).
Since the confidence interval (1.55, 4.20) contains the value 2, we can conclude that:
- The confidence interval does contain \( \mu_0 \) (where \( \mu_0 = 2 \)).
- This means that we cannot reject \( H_{0} \) at the 0.05 level because the null hypothesis value is a plausible value within the range of the confidence interval.
Putting it all together, we have:
Since the 95% confidence interval does contain \( \mu_0 \), then \( H_{0} \) cannot be rejected at the 0.05 level.