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Finding the Third Proportional to 389 and 687

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Solution

The third proportional to 389 and 687 is: 1,213.29

Step by Step Solution

  1. Step 1: Write the proportion equation
    389 : 687 = 687 : x
  2. Step 2: Convert to fraction form
    389/687 = 687/x
  3. Step 3: Cross multiply
    389x = 687 × 687
  4. Step 4: Simplify right side
    389x = 471,969
  5. Step 5: Solve for x
    x = 471,969/389
  6. Step 6: Final answer
    x = 1,213.29

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Why These Related Problems?

These problems maintain the same ratio (1.77) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.