Question 169808
Write a system of equations to solve the following problem. Be sure to identify what the variables represent. Then find the solution. 
Ms. Jones purchased a total of $45,000 in stocks, bonds, and money market funds.
Value Equation: s + b + m = 45000
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 The total she invested in bonds and money market funds was twice the amount she invested in stocks.
Value Equation: b+m = 2s
or 2s - b -m = 0
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 The return rates on the stocks, bonds, and money market funds were 10.0%, 7.0%, and 7.5%, respectively. The total value of the return was $3,660.
Interest Equation: 0.10s + 0.07b + 0.075m = 3600
or 10s + 7b + 75m = 360000
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 How much of each investment (stocks, bonds, and money market funds) did Ms. Jones purchase? 
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You have 3 equations with three variables:
 s  + b  +   m = 45000
2s  - b  -   m = 0
10s + 7b + 75m = 360000
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Solve using any system you know to get:
s = 15000
b = 30000
m = 0000
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Cheers,
Stan H.