1. **State the problem:** We need to write functions modeling the maximal oxygen consumption for two 25-year-old female athletes, where consumption decreases by 0.5% per year after age 25. 2. **Understand the problem:** The maximal oxygen consumption decreases by 0.5% per year, which means each year the consumption is multiplied by $1 - 0.005 = 0.995$. 3. **Define variables:** Let $x$ be the number of years after age 25. 4. **Write the function for the first athlete:** - Initial consumption at age 25 is 4 liters per minute. - Each year, consumption is multiplied by $0.995$. So the function is: $$f(x) = 4 \times 0.995^x$$ 5. **Write the function for the second athlete:** - Initial consumption at age 25 is 3.5 liters per minute. - Each year, consumption is multiplied by $0.995$. So the function is: $$g(x) = 3.5 \times 0.995^x$$ 6. **Summary:** - First athlete: $f(x) = 4 \times 0.995^x$ - Second athlete: $g(x) = 3.5 \times 0.995^x$ These functions model the maximal oxygen consumption in liters per minute $x$ years after age 25.