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Finding the Fourth Proportional to 686.80, 1,031.40 and 665.20

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Solution

The fourth proportional to 686.80, 1,031.40 and 665.20 is: 998.96

Step by Step Solution

  1. Step 1: Write the proportion equation
    686.80 : 1,031.40 = 665.20 : x
  2. Step 2: Convert to fraction form
    686.80/1,031.40 = 665.20/x
  3. Step 3: Cross multiply
    686.80x = 1,031.40 × 665.20
  4. Step 4: Simplify right side
    686.80x = 686,087.28
  5. Step 5: Solve for x
    x = 686,087.28/686.80
  6. Step 6: Final answer
    x = 998.96

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Why These Related Problems?

These problems maintain the same ratio (1.50) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.