Question 1123789
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<pre>
Let x be the amount Susan invested at 7%.

Then the amount invested at 11% is 3x dollars.


Your equation is


    0.07x + 0.11*(3x) = 1600.


    0.07x + 0.33x = 1600


    0.4x = 1600  ====>  x = {{{1600/0.4}}} = 4000 dolars.


<U>Answer</U>.  $4000  at  7%  and  $12000  at 11%.


<U>Check</U>.   0.07*4000 + 0.11*12000 = 1600 dollars.    ! Correct !
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Solved.