The computer club invested $2200, part at 4.5% interest and the rest at 7%. The total annuel interest earned was $144. How much was invested at each rate?
Let's assign a variable to represent the amount invested at 4.5% interest. Let's call it "x".
The amount invested at 7% interest can be represented by the expression "(2200 - x)" since it is the remainder of the total investment after subtracting the amount invested at 4.5%.
The interest earned on the amount invested at 4.5% is given by the equation "0.045x" (since 4.5% is equivalent to 0.045).
The interest earned on the amount invested at 7% is given by the expression "0.07(2200 - x)" (since 7% is equivalent to 0.07).
According to the problem, the total annual interest earned is $144. So, we can set up the equation:
0.045x + 0.07(2200 - x) = 144
Now let's solve for x:
To find out how much was invested at each interest rate, let's use a system of equations.
Let's assume that the amount invested at 4.5% interest rate is x, and the amount invested at 7% interest rate is (2200 - x), considering that the total amount invested is $2200.
Now, we can set up the equation for the total interest earned:
0.045x + 0.07(2200 - x) = 144
Let's solve this equation step by step:
0.045x + 154 - 0.07x = 144
Combining like terms:
-0.025x + 154 = 144
Subtracting 154 from both sides:
-0.025x = -10
Dividing by -0.025:
x = -10 / -0.025
x = 400
So, $400 was invested at a 4.5% interest rate, and the remaining amount ($2200 - $400 = $1800) was invested at a 7% interest rate.
Therefore, the computer club invested $400 at 4.5% interest and $1800 at 7% interest.