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Question 3 of 18

Use the compound-interest formula to find the account balance [tex]\( A \)[/tex], where [tex]\( P \)[/tex] is principal, [tex]\( r \)[/tex] is interest rate, [tex]\( n \)[/tex] is number of compounding periods per year, and [tex]\( t \)[/tex] is time in years.

\begin{tabular}{|c|c|c|c|}
\hline
[tex]$P$[/tex] & [tex]$r$[/tex] & compounded & [tex]$t$[/tex] \\
\hline
\[tex]$51,445 & $[/tex]4 \frac{1}{2} \%[tex]$ & Quarterly & $[/tex]7 \frac{1}{2}$ \\
\hline
\end{tabular}

Sagot :

Sure, let's walk through each step to find the account balance using the compound-interest formula. The formula for compound interest is:

[tex]\[ A = P \left(1 + \frac{r}{n}\right)^{nt} \][/tex]

Where:
- [tex]\( A \)[/tex] is the account balance after time [tex]\( t \)[/tex]
- [tex]\( P \)[/tex] is the principal amount (initial investment)
- [tex]\( r \)[/tex] is the annual interest rate (expressed as a decimal)
- [tex]\( n \)[/tex] is the number of compounding periods per year
- [tex]\( t \)[/tex] is the time the money is invested for in years

Given:
- [tex]\( P = \$51,445 \)[/tex]
- [tex]\( r = 4 \frac{1}{2}\% = 4.5\% = 0.045 \)[/tex] (as a decimal)
- Compounding is Quarterly, so [tex]\( n = 4 \)[/tex]
- [tex]\( t = 7 \frac{1}{2} \)[/tex] years = 7.5 years

Now, plug these values into the formula:

[tex]\[ A = 51445 \left(1 + \frac{0.045}{4}\right)^{4 \cdot 7.5} \][/tex]

Breaking it down:
1. Calculate [tex]\( \frac{r}{n} = \frac{0.045}{4} = 0.01125 \)[/tex]
2. Add 1 to this value: [tex]\( 1 + 0.01125 = 1.01125 \)[/tex]
3. Raise this result to the power of [tex]\( nt \)[/tex]:
[tex]\[ (1.01125)^{4 \times 7.5} = (1.01125)^{30} \][/tex]

4. Finally, multiply this result by [tex]\( P \)[/tex]:
[tex]\[ A = 51445 \times (1.01125)^{30} = 51445 \times 1.39856 = 71961.33475973115 \][/tex]

So, the account balance [tex]\( A \)[/tex] after 7.5 years is approximately \$71,961.33.