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Problem 1263

$$\$ 10,000$$ is to be invested for one year. A part of the $$\$ 10,000$$ is invested at \(6 \%\) and the remainder at \(7 \%\). The income from the $$\$ 10,000$$ is $$\$ 640$$ per year. Find the amount invested at each rate.

Short Answer

Expert verified
The amount invested at 6% is $$\$ 6,000$$ and the amount invested at 7% is $$\$ 4,000$$.
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Step 1: Assigning Variables

Let x be the amount invested at 6%, and y be the amount invested at 7%. Our goal is to find the values of x and y.

Step 2: Set up the system of linear equations

First, since the total investment is $10,000, we can write that as the sum of the amount invested at 6% and the amount invested at 7%. That gives us the first equation: \(x + y = 10000\) Now, we know that the total income is $640. The income from the amount invested at 6% is 6% of x, or \(\frac{6}{100}x\). The income from the amount invested at 7% is 7% of y, or \(\frac{7}{100}y\). So the total income can be represented as: \(\frac{6}{100}x + \frac{7}{100}y = 640\)

Step 3: Solve the system of linear equations

Now we have two equations with two variables. Our system of linear equations looks like this: 1) \(x + y = 10000\) 2) \(\frac{6}{100}x + \frac{7}{100}y = 640\) To solve the system, we can first multiply equation (2) by 100 to get rid of the fractions: 2) \(6x + 7y = 64000\) Now we can solve equation (1) for x: \(x = 10000 - y\) And substitute this expression back into equation 2: \(6(10000 - y) + 7y = 64000\)

Step 4: Solve for y

Now we have an equation with one variable: \(60000 - 6y + 7y = 64000\) Solve for y: \(y = 4000\)

Step 5: Find x

Now we know the value of y, we can plug it back into the expression for x: \(x = 10000 - 4000\) \(x = 6000\)

Step 6: Interpret the result

We have found that \(x = 6000\) and \(y = 4000\). This means that $$\$ 6,000$$ was invested at 6% and $$\$ 4,000$$ was invested at 7%.

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