1. **State the problem:** We want to test if the average age of COVID-19 Delta variant fatalities among senior citizens is less than 70 years. 2. **Set up hypotheses:** - Null hypothesis $H_0$: $\mu = 70$ (mean age is 70) - Alternative hypothesis $H_a$: $\mu < 70$ (mean age is less than 70) 3. **Given data:** - Sample size $n = 100$ - Sample mean $\bar{x} = 61.7$ - Sample standard deviation $s = 4.32$ - Significance level $\alpha = 0.05$ 4. **Test statistic formula:** $$ t = \frac{\bar{x} - \mu_0}{s / \sqrt{n}} $$ where $\mu_0 = 70$ is the hypothesized mean. 5. **Calculate the test statistic:** $$ t = \frac{61.7 - 70}{4.32 / \sqrt{100}} = \frac{-8.3}{0.432} \approx -19.21 $$ 6. **Determine critical value:** For a left-tailed test with $\alpha = 0.05$ and $df = n-1 = 99$, the critical t-value is approximately $-1.66$. 7. **Decision rule:** If $t < -1.66$, reject $H_0$. 8. **Conclusion:** Since $-19.21 < -1.66$, we reject the null hypothesis. This indicates strong evidence that the average age of fatalities is less than 70 years, meaning fatalities among senior citizens are getting younger. **Final answer:** The data suggests the average age is significantly less than 70 at the 0.05 significance level.