To solve this problem, we will use the following formulas:
(a) Formula for the annual interest
Where:
• P_N is the balance in the account after N years,
,
• P_0 is the starting balance of the account (also called an initial deposit, or principal),
,
• r is the annual interest rate in decimal form,
,
• k is the number of compounding periods in one year
(b) Formula for the annual interest compounded continuously
Where:
• P_N is the balance in the account after N years,
,
• P_0 is the starting balance of the account (also called an initial deposit, or principal),
,
• r is the annual interest rate in decimal form.
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We will compute the balanced of each investment, and then we will sum the results to get the total balance of each son.
1) Balance of Albert’s $2000 after 10 years
1-i) $1000 earned 1.2% annual interest compounded monthly
We use the (a) formula with the values: N = 10, P_0 = 1000, r = 1.2/100 = 0.012, k = 12.
1-ii) $500 lost 2% over the course of the 10 years
1-iii) $500 grew compounded continuously at a rate 0.8% annually
We use the (b) formula with the values: N = 10, P_0 = 500, r = 0.8/100 = 0.008.
Summing all Albert's investments, we get:
After 10 years, Albert's balance is $2159.07.
2) Balance of Marie’s $2000 after 10 years
2-i) $1500 earned 1.4% annual interest compounded quarterly
We use the (a) formula with the values: N = 10, P_0 = 1500, r = 1.4/100 = 0.014, k = 4.
2-ii) $500 gained 4% over the course of 10 years
Summing all Marie's investments, we get:
After 10 years, Marie's balance is $2244.99.
3) Balance of Hans’s $2000 after 10 years
$2000 grew compounded continuously at a rate of 0.9% annually
We use the (b) formula with the values: N = 10, P_0 = 2000, r = 0.9/100 = 0.009.
After 10 years, Hans's balance is $2188.35.
4) Balance of Max’s $2000 after 10 years
4-i) $1000 decreased in value exponentially at a rate of 0.5% annually
We use the (b) formula with the values: N = 10, P_0 = 1000, r = -0.5/100 = -0.005.
4-ii) $1000 earned 1.8% annual interest compounded biannually (twice a year)
We use the (a) formula with the values: N = 10, P_0 = 1000, r = 1.8/100 = 0.018, k = 2.
Summing all Max's investments, we get:
After 10 years, Max's balance is $2147.48.
5) From the results above, we see that Marie's balance is the highest. So Marie is 10,000 richer at the end of the competition.
Answers
0. After 10 years, Albert's balance is $2159.07.
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1. After 10 years, Marie's balance is $2244.99.
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2. After 10 years, Hans's balance is $2188.35.
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3. After 10 years, Max's balance is $2147.48.
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4. Marie is 10,000 richer at the end of the competition.