Molly invested $50,000 in various stocks and bonds. she earned 15% on the bonds and 18% on the stocks. If molly's total profit on both types of investment was $8,700, how much of the $50,000 did she invest in bonds?

1 answer

Let's define two variables to represent the amounts Molly invested in stocks and bonds:

- Let \( x \) be the amount Molly invested in bonds.
- Let \( y \) be the amount Molly invested in stocks.

From the problem statement, we know two things:
1. The total amount invested in both stocks and bonds is $50,000.
2. The total profit from both investments is $8,700.

These can be represented by the following system of equations:

1. \( x + y = 50,000 \)
2. \( 0.15x + 0.18y = 8,700 \)

We need to solve this system to find the value of \( x \) (the amount invested in bonds).

We start by solving the first equation for \( y \):

\[ y = 50,000 - x \]

Next, let's substitute this expression for \( y \) in the second equation:

\[ 0.15x + 0.18(50,000 - x) = 8,700 \]

Distribute \( 0.18 \) in the equation:

\[ 0.15x + 9,000 - 0.18x = 8,700 \]

Combine like terms:

\[ -0.03x + 9,000 = 8,700 \]

Subtract \( 9,000 \) from both sides of the equation to isolate the term with \( x \):

\[ -0.03x = -300 \]

Divide both sides by \( -0.03 \):

\[ x = \frac{-300}{-0.03} \]

\[ x = 10,000 \]

So, Molly invested $10,000 in bonds.

To verify, let's calculate the amount she invested in stocks:

\[ y = 50,000 - x \]
\[ y = 50,000 - 10,000 \]
\[ y = 40,000 \]

Now let's check the total profit calculation:
\[ 0.15 \times 10,000 + 0.18 \times 40,000 \]
\[ 1,500 + 7,200 = 8,700 \]

The calculations are correct. Therefore, Molly invested $10,000 in bonds.