If [tex]f(4) = 246.4[/tex] when [tex]r = 0.04[/tex] for the function [tex]f(t) = \rho e^t[/tex], then what is the approximate value of [tex]D[/tex]?

A. 1220
B. 210
C. 50
D. [tex]28\%[/tex]

Answer :

Sure! Let's solve the problem step-by-step.

We are given the function [tex]\( f(t) = D \cdot e^{rt} \)[/tex] and told that [tex]\( f(4) = 246.4 \)[/tex] when [tex]\( r = 0.04 \)[/tex].

To find the value of [tex]\( D \)[/tex], let's follow these steps:

1. Understand the Function: The function involved here is an exponential function where [tex]\( f(t) = D \cdot e^{rt} \)[/tex].

2. Substitute Known Values: We are given that when [tex]\( t = 4 \)[/tex], [tex]\( f(4) = 246.4 \)[/tex] and [tex]\( r = 0.04 \)[/tex]. Plug these into the equation:

[tex]\[
246.4 = D \cdot e^{0.04 \times 4}
\][/tex]

3. Calculate the Exponential Part: First, compute the exponent:

[tex]\[
0.04 \times 4 = 0.16
\][/tex]

So, we need to calculate [tex]\( e^{0.16} \)[/tex].

4. Solve for [tex]\( D \)[/tex]: The equation becomes:

[tex]\[
246.4 = D \cdot e^{0.16}
\][/tex]

To isolate [tex]\( D \)[/tex], divide both sides by [tex]\( e^{0.16} \)[/tex]:

[tex]\[
D = \frac{246.4}{e^{0.16}}
\][/tex]

5. Estimate [tex]\( D \)[/tex]: Once you compute [tex]\( e^{0.16} \)[/tex], use this to find the approximate value of [tex]\( D \)[/tex].

When you compute this, you'll find that [tex]\( D \approx 210 \)[/tex].

correct answer to the problem is (B) 210.