jake jenkins earned 9000 last year by giving tennis lessons. he invested part at 7% simple interest and the rest at 4%. he earned a total of 540 in interest. how much did he invest at 4%
x+ y = 9000
.07x + .04y =540
x = amt at 7% and y= amt at 4%
x + y = 9000
7x+4y = 54000
-7x -7y =-63000
-3y = -9000
y=3000
To find out how much Jake Jenkins invested at 4%, we can set up an equation.
Let's assume the amount invested at 7% is x (in dollars).
Therefore, the amount invested at 4% would be (9000 - x) dollars.
Now, we know that the interest earned from the 7% investment is given by:
0.07 * x
Similarly, the interest earned from the 4% investment is given by:
0.04 * (9000 - x)
The total interest earned is $540, so our equation becomes:
0.07 * x + 0.04 * (9000 - x) = 540
To solve this equation, let's simplify it:
0.07x + 360 - 0.04x = 540
0.03x = 540 - 360
0.03x = 180
Now, we can divide both sides of the equation by 0.03 to isolate x:
x = 180 / 0.03
x = 6000
Therefore, Jake Jenkins invested $6000 at 7% interest, and since the total amount he invested is $9000, the amount invested at 4% would be:
9000 - 6000 = $3000.
So, Jake Jenkins invested $3000 at 4%.