P Value Proportion D4011B
1. **State the problem:** We want to find the p-value for a one-sample z-test for proportions where the null hypothesis is $H_0: p = 0.75$ and the alternative hypothesis is $H_a: p \neq 0.75$. The sample size is $n=90$ and the sample proportion is $\hat{p} = 0.82$.
2. **Formula for the test statistic:** The z-test statistic for a proportion is given by
$$
z = \frac{\hat{p} - p_0}{\sqrt{\frac{p_0(1-p_0)}{n}}}
$$
where $p_0$ is the hypothesized population proportion.
3. **Calculate the standard error:**
$$
SE = \sqrt{\frac{0.75 \times (1 - 0.75)}{90}} = \sqrt{\frac{0.75 \times 0.25}{90}} = \sqrt{\frac{0.1875}{90}} = \sqrt{0.0020833} \approx 0.0456
$$
4. **Calculate the z statistic:**
$$
z = \frac{0.82 - 0.75}{0.0456} = \frac{0.07}{0.0456} \approx 1.54
$$
5. **Find the p-value:** Since this is a two-tailed test, the p-value is
$$
p\text{-value} = 2 \times P(Z > 1.54)
$$
Using standard normal tables or a calculator,
$$
P(Z > 1.54) \approx 0.0618
$$
So,
$$
p\text{-value} = 2 \times 0.0618 = 0.1236
$$
6. **Interpretation:** The p-value is approximately 0.124, which means there is about a 12.4% chance of observing a sample proportion as extreme as 0.82 if the true proportion is 0.75.
**Final answer:**
$$
p\text{-value} \approx 0.124
$$