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Michelle deposited $1,600 into an account that is compounded continuously with an annual interest rate of 8%. After t years, there was $3,200 in the account. Based on the given information, if the formula for continuously compounded interest is A = P e r t , where P represents the initial amount of money, r represents the annual interest rate (as a decimal), t represents the number of years, and A represents the amount of money after t years, how many years had the money been in the account? Express your answer as a logarithm.

Sagot :

Answer:

As a logarithm, the money had been in the account for [tex]t = \frac{\ln{2}}{0.08}[/tex] years.

Step-by-step explanation:

The amount of money in the account after t years is given by:

[tex]A(t) = Pe^{rt}[/tex]

In which P is the initial amount deposited and r is the interest rate, as a decimal.

Michelle deposited $1,600 into an account that is compounded continuously with an annual interest rate of 8%.

This means that [tex]P = 1600, r = 0.08[/tex]

After t years, there was $3,200 in the account. How many years had the money been in the account?

This is t for which [tex]P(t) = 3200[/tex]. So

[tex]A(t) = Pe^{rt}[/tex]

[tex]3200 = 1600e^{0.08t}[/tex]

[tex]e^{0.08t} = \frac{3200}{1600}[/tex]

[tex]e^{0.08t} = 2[/tex]

[tex]\ln{e^{0.08t}} = \ln{2}[/tex]

[tex]0.08t = \ln{2}[/tex]

[tex]t = \frac{\ln{2}}{0.08}[/tex]

[tex]t = 8.67[/tex]

As a logarithm, the money had been in the account for [tex]t = \frac{\ln{2}}{0.08}[/tex] years.

The value of time t is [tex]\frac{ln(2)}{0.08}[/tex].

Given: P=1600

r=8%=0.08

t = ?

A=3200

Using the given compound interest formula we get:

[tex]A=Pe^{rt}\\3200=1600e^{0.08t}\\2=e^{0.08t}\\[/tex]

Take ln on both sides,

[tex]ln(2)=ln(e^{0.08t})\\ln(2)=0.08t\\t=\frac{ln(2)}{0.08}[/tex]

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