Comparing types of interest

A newly hired lawyer receives a $15,000 signing bonus from a law firm and invests the money in a savings account at 4.75% interest. After 42 months, the lawyer checks the account balance.

Part A: Calculate the interest earned, to the nearest dollar, if the interest is compounded quarterly. Show all work. (2 points)

Part B: Calculate the interest earned, to the nearest dollar, if the interest is compounded continuously. Show all work. (2 points)

Part C: Using the values from Part A and Part B, compare the interest earned for each account. (1 point)

Respuesta :

Answer:

A)   $2,695.69

B)   $2,713.02

C)   See below.

Step-by-step explanation:

Part A

[tex]\boxed{\begin{minipage}{8.5 cm}\underline{Compound Interest Formula}\\\\$ I=P\left[\left(1+\frac{r}{n}\right)^{nt}-1\right]$\\\\where:\\\\ \phantom{ww}$\bullet$ $I =$ interest accrued \\ \phantom{ww}$\bullet$ $P =$ principal amount \\ \phantom{ww}$\bullet$ $r =$ interest rate (in decimal form) \\ \phantom{ww}$\bullet$ $n =$ number of times interest is applied per year \\ \phantom{ww}$\bullet$ $t =$ time (in years) \\ \end{minipage}}[/tex]

Given:

  • P = $15,000
  • r = 4.75% = 0.0475
  • n = 4 (quarterly)
  • t = 42 months = 3.5 years

Substitute the given values into the compound interest formula and solve for I:

[tex]\implies I=15000\left[\left(1+\dfrac{0.0475}{4}\right)^{4 \times 3.5}-1\right][/tex]

[tex]\implies I=15000\left[\left(1.011875\right)^{14}-1\right][/tex]

[tex]\implies I=15000(0.179712348...)[/tex]

[tex]\implies I=2695.68522...[/tex]

Therefore the interest earned is $2,695.69 to the nearest dollar.

Part B

[tex]\boxed{\begin{minipage}{8.5 cm}\underline{Continuous Compounding Interest Formula}\\\\$ I=P\left(e^{rt}-1\right)$\\\\where:\\\\ \phantom{ww}$\bullet$ $I =$ interest accrued \\\phantom{ww}$\bullet$ $P =$ principal amount \\\phantom{ww}$\bullet$ $e =$ Euler's number (constant) \\\phantom{ww}$\bullet$ $r =$ annual interest rate (in decimal form) \\\phantom{ww}$\bullet$ $t =$ time (in years) \\\end{minipage}}[/tex]

Given:

  • P = $15,000
  • r = 4.75% = 0.0475
  • t = 42 months = 3.5 years

Substitute the given values into the continuous interest formula and solve for I:

[tex]\implies I=15000\left(e^{0.0475 \times 3.5}-1\right)[/tex]

[tex]\implies I=15000\left(e^{0.16625}-1\right)[/tex]

[tex]\implies I=15000\left(0.180868281...\right)[/tex]

[tex]\implies I=2713.02422...[/tex]

Therefore the interest earned is $2,713.02 to the nearest dollar.

Part C

The difference between the interest earned for the two accounts is:

[tex]\implies 2713.02-2695.69=17.33[/tex]

Therefore, the principal will earn $17.33 more interest if the interest is compounded continuously rather than compounded quarterly.