Question

9. Read the following word problem, then create a linear equation to model the problem. Provide work to show how your linear equation models the problem, such as a brief description, a picture, or a table. Finally, use the linear equation you created to solve the problem.

$2400 is divided between two accounts. One account pays 2% interest, while the other account pays 3.5% interest. At the end of one interest period, the interest earned is $81. How much was invested in each account?

Answer 1

$200 at 2%.

$2200 at 3.5%.

Explanation:

Let the two amounts be x and y.

x earns 2% interest, and y earns 3.5% interest.

Since the total is $2400, then

x + y = 2400

Now we can solve for y and express the second amount in terms of x.

y = 2400 - y

The two amounts are x and 2400 - x.

In one interest period, the amount of interest earned is the amount of money in the account multiplied by the interest.

2% = 0.02; 3.5% = 0.035

The x amount earns 0.02x interest.

The y amount earns 0.035y interest.

The total interest earned is the sum of the interest amounts of the two accounts.

0.02x + 0.035y

We now replace y with 2400 - x, and we set the sum of the interest amounts equal to the total interest earned, $81.

0.02x + 0.035(2400 - x) = 81

The equation above is the linear equation.

Now we solve it. Distribute on the left side.

0.02x + 84 - 0.035x = 81

Combine like terms on the left side.

-0.015x + 84 = 81

Subtract 84 from both sides.

-0.015x = -3

Divide both side by -0.015.

x = 200

$200 was deposited in the account earning 2%.

y = 2400 - x

y = 2400 - 200

y = 2200

$2200 was deposited in the account earning 3.5%.