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4) Miguel found a savings account that his late grandmother had opened, but had forgotten about. She haddeposited $4,500 at 2.5% compounded yearly. When Tito checked the balance, there was $22,960.83 in theaccount.How long had the money been in the savings account, gathering interest?

Sagot :

The formula for compound interest would be:

[tex]A=P(1+r)^t[/tex]

Where

A is the amount accumulated after a time

P is the principal amount deposited

r is the rate of interest (in decimal)

t is the time in years

Given,

P = 4500

r = 2.5%/100 = 0.025

A = 22,960.83

Now, we substitute and solve for t using natural logs. Shown below:

[tex]\begin{gathered} A=P(1+r)^t \\ 22,960.83=4500(1+0.025)^t \\ 22,960.83=4500(1.025)^t \\ 5.1024=1.025^t \end{gathered}[/tex]

Now, we take natural log (Ln) of both sides and solve for t :

[tex]\begin{gathered} \ln (5.1024)=\ln (1.025^t) \\ \ln (5.1024)=t\ln (1.025) \\ t=\frac{\ln (5.1024)}{\ln (1.025)} \\ t=65.99 \end{gathered}[/tex]

So, the money was approximately 66 years old.