Question: According to the U.S. Census Bureau, about $78\%$ of Americans are adults ($18$ and over). Use the U.S. population estimate of $330$ million people to calculate the number of American adults in $2020$. Round to the nearest hundred thousand adults.
1. **State the problem:** We need to find the number of American adults in 2020 given that $78\%$ of the population are adults and the total population is $330$ million.
2. **Formula:** To find the number of adults, multiply the total population by the percentage of adults:
$$\text{Number of adults} = \text{Total population} \times \frac{\text{Percentage of adults}}{100}$$
3. **Substitute values:**
$$\text{Number of adults} = 330,000,000 \times \frac{78}{100}$$
4. **Calculate:**
$$330,000,000 \times 0.78 = 257,400,000$$
5. **Rounding:** Round $257,400,000$ to the nearest hundred thousand:
The hundred thousand digit is $4$ (in $257,400,000$), and the digit after it is $0$, so we round down.
Final rounded number:
$$257,400,000$$
**Answer:** There are approximately $257,400,000$ American adults in 2020.