SOLUTION: Walt made an extra $10,0000 last year from a part-time job. He invested part of the money at 8% and the rest at 7%. He made a total of $760 in interest. How much was invested at 7%

Question 64817: Walt made an extra $10,0000 last year from a part-time job. He invested part of the money at 8% and the rest at 7%. He made a total of $760 in interest. How much was invested at 7%?
Answer by tutorcecilia(2152) (Show Source): You can put this solution on YOUR website!
Use the standard equation of a line:
Ax+By=C
and
x+y=C
So, x+(C-x)=C
.
7%x+8%y=760
So, .07x+.08(10,000-x)=760 [change percentages to decimals]
.07x+800-.08x=760 [solve for x]
-.01x=-800+760
-.01x=-40
x=-40/-.01
x=$4,000 invested at 7%
$10,000-4,000=$6000 invested at 8%
.
check by plugging in all of the values back into the original equation:
.07(4,000)+.08(10,000-(4,000))=760
760=760 [checks out]

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