Difference between revisions of "022 Sample Final A, Problem 10"
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(Created page with "<span class="exam">Set up the formula to find the amount of money one would have at the end of 8 years if she invests $2100 in an account paying 6% annual interest, compounded...") 

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::<math>A\,=\,P\left(1+\frac{r}{n}\right)^{nt},</math>  ::<math>A\,=\,P\left(1+\frac{r}{n}\right)^{nt},</math>  
    
−  where <math style="verticalalign: 0%;">A</math> is the value of the account, <math style="verticalalign: 0%;">P</math> is the principal (original amount invested), <math style="verticalalign: 0%;">r</math> is the annual rate and <math style="verticalalign: 0%;">n</math> is the number of compoundings per year. The value of <math style="verticalalign: 0%;">n</math> is <math style="verticalalign: 0%;">365</math> for compounding daily, <math style="verticalalign: 0%;">52</math> for compounding weekly, and <math style="verticalalign:   +  where <math style="verticalalign: 0%;">A</math> is the value of the account, <math style="verticalalign: 0%;">P</math> is the principal (original amount invested), <math style="verticalalign: 0%;">r</math> is the annual rate and <math style="verticalalign: 0%;">n</math> is the number of compoundings per year. The value of <math style="verticalalign: 0%;">n</math> is <math style="verticalalign: 0%;">365</math> for compounding daily, <math style="verticalalign: 0%;">52</math> for compounding weekly, and <math style="verticalalign: 1px">12</math> for compounding monthly. As a result, the exponent <math style="verticalalign: 0%;">nt</math>, where <math style="verticalalign: 0%;">t</math> is the time in years, is the number of compounding periods where we actually earn interest. Similarly, <math style="verticalalign: 22%;">r/n</math> is the rate per compounding period (the annual rate divided by the number of compoundings per year). 
    
For example, if we compound monthly for <math style="verticalalign: 0%;">7</math> years at a <math style="verticalalign: 5%;">6%</math> rate, we would compound <math style="verticalalign: 5%;">nt\,=\,12 \cdot7\,=\,84</math> times, once per month, at a rate of <math style="verticalalign: 22%;">0.06/12\,=\,0.005</math> per monthly period. Notice that we <u>'''always'''</u> use the decimal version for interest rates when using these equations.  For example, if we compound monthly for <math style="verticalalign: 0%;">7</math> years at a <math style="verticalalign: 5%;">6%</math> rate, we would compound <math style="verticalalign: 5%;">nt\,=\,12 \cdot7\,=\,84</math> times, once per month, at a rate of <math style="verticalalign: 22%;">0.06/12\,=\,0.005</math> per monthly period. Notice that we <u>'''always'''</u> use the decimal version for interest rates when using these equations. 
Latest revision as of 17:24, 6 June 2015
Set up the formula to find the amount of money one would have at the end of 8 years if she invests $2100 in an account paying 6% annual interest, compounded quarterly.
Foundations: 

The primary purpose of this problem is to demonstrate that you understand compounding on an interval of time. When we compound on an interval, say monthly, the value in the account only changes at the end of each interval. In other words, there is no interest accrued for a week or a day. As a result, we use the formula 

where is the value of the account, is the principal (original amount invested), is the annual rate and is the number of compoundings per year. The value of is for compounding daily, for compounding weekly, and for compounding monthly. As a result, the exponent , where is the time in years, is the number of compounding periods where we actually earn interest. Similarly, is the rate per compounding period (the annual rate divided by the number of compoundings per year). 
For example, if we compound monthly for years at a rate, we would compound times, once per month, at a rate of per monthly period. Notice that we always use the decimal version for interest rates when using these equations. 
Solution: 

We are given all the pieces required. We begin with of principal, and compound quarterly, or times per year. Using the formula in 'Foundations', the equation for the account value after 8 years is 

Final Answer: 

