Question 975078
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The first thing you need to do is to calculate how much money was invested at interest.


Calculate 20% of $10,000.  Then subtract that amount from $10,000 to determine the amount that was invested at interest for the son's education fund.  I'll let you do that arithmetic.  In the meantime, until you calculate the amount, we can call the amount invested *[tex \LARGE P] meaning the present value of the investment.


Let *[tex \LARGE x] represent the portion of the amount *[tex \LARGE P] that was invested at 7%.  Then the portion that was invested at 4% must be *[tex \LARGE (P\ -\ x)].


The actual amount of interest earned on *[tex \LARGE x] dollars invested at 7% simple interest is *[tex \LARGE 0.07x].  The actual amount of interest earned on *[tex \LARGE P\ -\ x] dollars invested at 4% simple interest is *[tex \LARGE 0.04(P\ -\ x)]. These two amounts add up to $480.00, hence:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ 0.07x\ +\ 0.04(P\ -\ x)\ =\ 480]


Once you have calculated the value of *[tex \LARGE P], substitute that amount into the equation and solve for *[tex \LARGE x], which will be the amount invested at 7%.  Subtract that amount from *[tex \LARGE P] which will be the amount invested at 4%.


John
*[tex \LARGE e^{i\pi}\ +\ 1\ =\ 0]
My calculator said it, I believe it, that settles it

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