SOLUTION: Here is the problem: Walt made an extra $12,000 last year from a part-time job. He invested part of the money at 7% and the rest at 9%. He made a total of $970 in intrest. How m

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons  -> Quadratic Equation Lesson -> SOLUTION: Here is the problem: Walt made an extra $12,000 last year from a part-time job. He invested part of the money at 7% and the rest at 9%. He made a total of $970 in intrest. How m      Log On


   

Question 180131: Here is the problem:
Walt made an extra $12,000 last year from a part-time job. He invested part of the money at 7% and the rest at 9%. He made a total of $970 in intrest. How much was invested at 7%?
I can honestly say that I am beyond stuck I don't even know where to start on this problem. Please Help!!! :-)
Answer by Mathtut(3670) About Me  (Show Source):
You can put this solution on YOUR website!
let x and y be amounts invested at 7% and 9% respectively
:
x + y = $12,000..................eq 1
x * 0.07 + y * 0.09 = $970.......eq 2
rewrite eq 1 to x = $12,000 - y and plug that value into eq 2
:
($12,000 - y) * 0.07 + y * 0.09 = $970
:
$840 - 0.07y + 0.09y = $970
:
0.02y = $130
$highlight%28y=6500%29invested at 9%
:
$highlight%28x=12000-6500=5500%29invested at 7%