Evaluate [tex]\(\frac{f(5)-f(1)}{5-1}\)[/tex] using the given table, and explain what it tells you about the US debt.

\begin{tabular}{|c|c|}
\hline
[tex]$t$[/tex] & [tex]$D$[/tex] (\$ billions) \\
\hline
0 & 5674.2 \\
1 & 5817.1 \\
2 & 6228.2 \\
3 & 6783.2 \\
4 & 7379.1 \\
5 & 7960.4 \\
6 & 8507.0 \\
7 & 9007.7 \\
8 & 10024.7 \\
\hline
\end{tabular}

Round your answer to one decimal place.

[tex]\[
\frac{f(5)-f(1)}{5-1} = \_\_\_\_ \, \text{billion per year}
\][/tex]



Answer :

First, let's understand the table provided. The table gives values of [tex]\( D = f(t) \)[/tex], which represent the total US debt in billions of dollars [tex]\( t \)[/tex] years after 2000.

To calculate the average rate of change of the US debt between the years corresponding to [tex]\( t = 1 \)[/tex] and [tex]\( t = 5 \)[/tex], we need to evaluate the expression [tex]\(\frac{f(5) - f(1)}{5 - 1}\)[/tex].

Let's break this down into steps:

1. Identify [tex]\( f(5) \)[/tex] and [tex]\( f(1) \)[/tex] from the table:
- [tex]\( f(1) = 5817.1 \)[/tex] billion dollars.
- [tex]\( f(5) = 7960.4 \)[/tex] billion dollars.

2. Substitute these values into the expression [tex]\(\frac{f(5) - f(1)}{5 - 1}\)[/tex]:
[tex]\[ \frac{f(5) - f(1)}{5 - 1} = \frac{7960.4 - 5817.1}{5 - 1} \][/tex]

3. Calculate the difference in the numerator:
[tex]\[ 7960.4 - 5817.1 = 2143.3 \][/tex]

4. Calculate the difference in the denominator:
[tex]\[ 5 - 1 = 4 \][/tex]

5. Compute the average rate of change:
[tex]\[ \frac{2143.3}{4} = 535.825 \][/tex]

6. Round the answer to one decimal place:
[tex]\[ 535.825 \approx 535.8 \][/tex]

Therefore, the average rate of change of the US debt from [tex]\( t = 1 \)[/tex] to [tex]\( t = 5 \)[/tex] is [tex]\( \boxed{535.8} \)[/tex] billion dollars per year.

This tells us that between the years corresponding to [tex]\( t = 1 \)[/tex] (which is year 2001) and [tex]\( t = 5 \)[/tex] (which is year 2005), the US debt increased on average by approximately [tex]\( 535.8 \)[/tex] billion dollars per year.