Question 1130191
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The amount of interest from the part at 8% was 4 times the amount of interest from the part at 6%.  The 8% rate is 4/3 of the 6% rate; to get 4 times as much interest, using an interest rate that is 4/3 as large, the amount at 8% must be 3 times the amount at 6%.  So<br>
let x = amount at 6%
then 3x = amount at 8%
and (92000-4x) = amount at 9%<br>
The total interest was $7200:<br>
{{{.06(x)+.08(3x)+.09(92000-4x) = 7200}}}
{{{.06x+.24x+8280-.36x = 7200}}}
{{{1080 = .06x}}}
{{{x = 1080/.06 = 18000}}}<br>
ANSWER: The amounts invested at each rate were<br>
6%: x = $18000
8%: 3x = $54000
9%: $92000-4x = $20000<br>
CHECK: {{{.06(18000)+.08(54000)+.09(20000) = 1080+4320+1800 = 7200}}}