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Here is the question for my homework:

A mother wants to invest $\$7000.00$ for her son's future education. She invests a portion of the money in a bank certificate of deposit (CD account) which earns $4\%$ and the remainder in a savings bond that earns $7\%$. If the total interest earned after one year is $\$420.00$, how much money was invested in the CD account?

Now, here is my steps:

Amount invested in the savings bond can be represented as $7000 - x$

The interest earned in one year on the CD account is $0.04x$

So, the interest earned on the savings bond in one year can be represented as: $0.07(7000-x)$

The total interested earned after one year is $\$420.00$

The equation is now $0.04x+0.07(7000-x) = 420.00$

Now to SIMPLFY it.

I have this so far

$n - 420 = 0.03x$

How do I get the number $n$?

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    Shouldn't your n just be the .07*7000 that you left out in your last line?2010-10-03
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    @Dan: The solution of your eq. $0.04x+0.07(7000-x)=420.00$ is $x=\frac{7000}{3}\approx 2333.33$. Since the LHS, $0.04x+0.07(7000-x)=490.0-0.03x$, you have the equivalent eq. $490.0-0.03x=420.00$ or $490.0-420.00=0.03x$, the solution of which is $x=\frac{490.0-420.00}{0.03}=\frac{7000}{3}\approx 2333.33$ USD.2010-10-03

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