help needed in math question?

4 ANSWERS

1. Guest2404
   

   interest = p * 18000 * 0.055 + (1-p) * 18000 * 0.04
   
   = 831
   
   => 270 p + 720 = 831
   
   => 270 p = 111
   
   => p = 0.4111111....
   
   So 41.111 % of the money was invested at 5.5 %
   
   or 7400 $. The rest (10600 $) was invested at 4 %.

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2. Guest3973
   

   $18,000 was invested, so split that into the two parts. $x amount was invested at 5.5% and ($18,000-x) was invested at 4%
   
   .055x + (18,000 - x).04 = 831
   
   .055x + 720 - .04x = 831
   
   .015x = 111
   
   x = 7,400
   
   $7,400 was invested at 5.5%
   
   $10,600 was invested at 4.0%
   
   Piece of cake.

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3. Guest6863
   

   let x and y be the two parts
   
   x + y = 18000
   
   x(0.055) + y(0.04) = 831
   
   x = 18000 - y
   
   (18000 - y)(0.055) + y(0.04) = 831
   
   990 - 0.055y + 0.04y = 831
   
   0.015y = 159
   
   y = 10600
   
   x = 7400
   
   Check
   
   7400(0.055) + 10600(0.04) = 831
   
   407 + 424 = 831
   
   .
   
   

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4. Guest7654
   

   x+y=18000
   
   .04x + .055y = 831
   
   .04x + .055(18000-x) = 831
   
   .04x + 990 - .055x = 831
   
   .015x = 159
   
   x = 10600
   
   y = 18000 - 10600 = 7400
   
   

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