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%.
Let the amount invested at 10% be: x
Then the amount invested at 8% is: 2x
The formula for simple interest is: {{{highlight(I=Prt)}}} 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(2x)+.10(x)}}}
{{{91=.16x+.10x}}}
{{{91=.26x}}}
{{{91/.26=.26x/.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!!!!