Confidence Interval A0981A
1. **State the problem:** We have a sample of 400 adults, with 180 believing their student loan debt is unmanageable. We want to find the degree of confidence for a confidence interval given as $0.45 \pm 0.04$.
2. **Identify the sample proportion:** The sample proportion $\hat{p}$ is calculated as:
$$\hat{p} = \frac{180}{400} = 0.45$$
3. **Recall the confidence interval formula for a proportion:**
$$\hat{p} \pm z \times \sqrt{\frac{\hat{p}(1-\hat{p})}{n}}$$
where $z$ is the z-score corresponding to the confidence level, and $n=400$ is the sample size.
4. **Given the margin of error (ME):**
$$ME = 0.04 = z \times \sqrt{\frac{0.45 \times 0.55}{400}}$$
5. **Calculate the standard error (SE):**
$$SE = \sqrt{\frac{0.45 \times 0.55}{400}} = \sqrt{\frac{0.2475}{400}} = \sqrt{0.00061875} \approx 0.02488$$
6. **Solve for $z$:**
$$z = \frac{ME}{SE} = \frac{0.04}{0.02488} \approx 1.607$$
7. **Find the confidence level corresponding to $z=1.607$:**
The confidence level is $2 \times P(Z \leq 1.607) - 1$.
Using standard normal distribution tables or a calculator:
$$P(Z \leq 1.607) \approx 0.946$$
So,
$$\text{Confidence level} = 2 \times 0.946 - 1 = 0.892 = 89.2\%$$
**Final answer:** The degree of confidence is approximately **89.2%**.