SOLUTION: I got three different answer can someone please put me on the right track thank you in advance. Walt made an extra $9000 last year from a part-time job. He invested part o

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Question 171715This question is from textbook
: I got three different answer can someone please put me on the right track
thank you in advance.

Walt made an extra $9000 last year from a part-time job. He invested part of the money at 9% and the rest at 8%. He made a total of $770 in interest. How much was invested at 8%?
This question is from textbook

Found 2 solutions by stanbon, ptaylor:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
Walt made an extra $9000 last year from a part-time job. He invested part of the money at 9% and the rest at 8%. He made a total of $770 in interest. How much was invested at 8%?
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Interest Equation: 0.08x + 0.09(9000-x) = 770
8x + 9(9000-x) = 77000
-x +81000 = 77000
x = 4000 (amount invested at 8%)
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Cheers,
Stan H.

Answer by ptaylor(2198) About Me  (Show Source):
You can put this solution on YOUR website!

Interest(I)=Principal(P)*Rate(R)*Time(T)
Let x=amount invested at 8%
Then 9000-x=amount invested at 9%
Interest at 8%=x*0.08*1=0.08x
Interest at 9%=(9000-x)*0.09*1=0.09(9000-x)
And we are told that the above interest adds up to 770, so:
0.08x+0.09(9000-x)=770 get rid of parens
0.08x+810-0.09x=770 subtract 810 from each side
0.08x+810-810-0.09x=770-810 collect like terms
-0.01x=-40 divide each side by-0.01
x=$4000--------------------amount invested at 8%
9000-x=9000-4000=$5000---------amount invested at 9%
CK
0.08*4000+0.09*5000=770
320+450=770
770=770
Hope this helps---ptaylor