Joshua invested $110 in an account paying an interest rate of 2 1/2% compounded annually. Zoey invested $110 in an account paying an interest rate of 2 5/8% compounded continuously. To the nearest dollar, how much money would Zoey have in her account when Joshua's money has doubled in value?

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Answer:

[tex]\large \boxed{\$229}}[/tex]

Step-by-step explanation:

1. Calculate the time for Joshua's investment to double

The formula for interest compounded annually is  

A = P(1 + r)ᵗ

where

A = Accrued Amount

P = Principal Amount

r =annual interest rate as a decimal

t = time in years

(a) Data

A = $220

P = $110

r =0.025

(b) Calculation

[tex]\begin{array}{rcl}A & = & P(1 + r)^{t}\\220 & = & 110(1+ 0.025)^{t}\\2 & = & 1.025^{t}\\\ln 2 & = & t \ln 1.025\\t & = & \dfrac{\ln 2}{\ln 1.025}\\\\t & = & \dfrac{0.6931}{0.02469}\\\\t & = & \textbf{28.07 yr}\\\\\end{array}[/tex]

It will take 28.07 yr for Joshua to double his investment.

2. Calculate the value of Zoey's investment

The formula for interest compounded continuously is

[tex]\begin{array}{rcl}A & = & Pe^{rt}\\& = & 110e^{0.02625\times 28.07}\\& = & 110e^{0.7368}\\& = & 110\times2.0893\\& = & \mathbf{\$229}\\\end{array}\\\text{Zoey will have $\large \boxed{\mathbf{\$229}}$ in her account by the time Joshua's money has doubled.}[/tex]