# Chapter 3 - Equations and Problem Solving - 3.5 - Problem Solving - Problem Set 3.5: 39

She invested 500 dollars at 4%. She invested 1000 dollars at 5%. She invested 1500 dollars at 6%.

#### Work Step by Step

Let X represent the sum of money invested at 4%. She earned 4% $\times$ X = 0.04X from this investment. She invested twice that sum at 5%. So, she invested 2X at 5%. She earned 5% $\times$ 2X = 0.1X from this investment. She invested three times that sum at 6%. So, she invested 3X at 6%. She earned 6% $\times$ 3X = 0.18X from this investment. Her total interest from all three investments was 160 dollars. We can set up the following equation: 0.04X + 0.1X + 0.18X = 160 0.32X = 160 Divide both sides by 0.32: X = 500 She invested 500 dollars at 4%. She invested twice that sum, or 500$\times$2 = 1000 dollars at 5%. She invested three times that sum, or 500$\times$ 3 = 1500 dollars at 6%.

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