SOLUTION: Mike invested $7000 for one year. He invested part of it at 8% and the rest at 21%. At the end of the year he earned $764 in interest. How much did he invest at each rate?

Question 190685: Mike invested $7000 for one year. He invested part of it at 8% and the rest at 21%. At the end of the year he earned $764 in interest. How much did he invest at each rate?

Found 3 solutions by nerdybill, jojo14344, checkley75:
Answer by nerdybill(5405)   (Show Source):
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Mike invested $7000 for one year. He invested part of it at 8% and the rest at 21%. At the end of the year he earned $764 in interest. How much did he invest at each rate?
.
Let x = amount invested at 8%
then
7000-x = amount invested at 21%
.
.08x + .21(7000-x) = 764
.08x + 1470 - .21x = 764
.08x - .21x = -706
- .13x = -706
x = $5430.77 (amount invested at 8%)
.
Amount invested at 21%:
7000-x = 7000-5430.77 = $1569.23

Answer by jojo14344(1512)   (Show Source):
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Let , x= amount inv. at 8%
And, $7,000 - x = amount inv. at 21%

It follows,
Interest at 8% + Interest at 21% = $764

---->
x = $5430.77 amount for 8%
And, $7,000 - $5430.77 = $1,569.23, amount for 21%

Check,

Thank you.
Jojo

Answer by checkley75(3666)   (Show Source):
You can put this solution on YOUR website!
.21x+.08(7,000-x)=764
.21x+560-.08x=764
.13x=764-560
.13x=204
x=204/.13
x=1,569.23 invested @ 21%.
7,000-1,569.23=5,430.77 invested @ 8%.
Proof:
.21*1,695.23+.08*5,430.77=764
329.54+434.46=764
764=764