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A loan of $43,000 is made at 5.25% interest, compounded annually. After how many years will the amount due reach $64,000 or more? (Use the calculator provided if necessary.)Write the smallest possible whole number answer.

User Eric Bock
by
3.1k points

1 Answer

12 votes
12 votes

Answer:

8 years

Explanation:

For a compound interest loan compounded annually, the amount due after t years is calculated using the formula:


A(t)=P(1+r)^t\text{ where }\begin{cases}P={Loan\;Amount} \\ {r=Annual\;Interest\;Rate}\end{cases}

We want to find when the amount due will reach $64,000 or more.


43000(1+0.0525)^t\geq64,000

The equation is solved for t:


\begin{gathered} \text{ Divide both sides by }43000 \\ (43,000(1+0.0525)^t)/(43000)\geqslant(64,000)/(43000) \\ (1.0525)^t\geq(64)/(43) \\ \text{Take the log of both sides:} \\ \log(1.0525)^t\geqslant\log((64)/(43)) \\ \text{By the power law of logarithm:} \\ \implies t\operatorname{\log}(1.0525)\geq\operatorname{\log}((64)/(43)) \\ \text{ Divide both sides by }\operatorname{\log}(1.0525) \\ t\geq\frac{\operatorname{\log}((64)/(43))}{\operatorname{\log}(1.0525)} \\ t\geq7.77 \end{gathered}

The number of years when the amount due will reach $64,000 or more is 8 years.

User Kushal Dave
by
2.9k points
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