SOLUTION: A certain sum of money is invested at 10%. Twice that amount is invested at 8%. The total amount of interest from both investments is $91. How much is invested at 8%.

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Question 76851: A certain sum of money is invested at 10%. Twice that amount is invested at 8%. The total amount of interest from both investments is $91. How much is invested at 8%.
Answer by funmath(2933) About Me  (Show Source):
You can put this solution on YOUR website!
A certain sum of money is invested at 10%. Twice that amount is invested at 8%. The total amount of interest from both investments is $91. How much is invested at 8%.
Let the amount invested at 10% be: x
Then the amount invested at 8% is: 2x
The formula for simple interest is: highlight%28I=Prt%29 I=interest, P=amount invested(known also as Principal) r=interest rate and t=time in years
Since they didn't give you time, I assume it is one year and can be ignored.
rate=8/100=.08 for 8%
rate=10/100=.10 for 10%
I=91
Problem to solve:
91=.08%282x%29%2B.10%28x%29
91=.16x%2B.10x
91=.26x
91%2F.26=.26x%2F.26
350=x
The amount invested at 10% is: x=$350
The amount invested at 8% is 2x=2($350)=$700 <--that's what they asked for.
Happy Calculating!!!!