Question 1167264
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Let x = invested at 7%


Then the amount invested at 3% is  (13000-x)  dollars.


The total interest equation is


    0.07x + 0.03*(13000-x) = 870  dollars.


From the equation


    x = {{{(870-0.03*13000)/(0.07-0.03)}}} = 12000.


<U>ANSWER</U>.  $12000 invested at 7% and the rest  $1000 invested at 3%.


<U>CHECK</U>.  0.07*12000 + 0.03*1000 = 870  dollars of total interest.  ! Correct !
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Solved.