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Finding the Third Proportional to 399 and 515

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Solution

The third proportional to 399 and 515 is: 664.72

Step by Step Solution

  1. Step 1: Write the proportion equation
    399 : 515 = 515 : x
  2. Step 2: Convert to fraction form
    399/515 = 515/x
  3. Step 3: Cross multiply
    399x = 515 × 515
  4. Step 4: Simplify right side
    399x = 265,225
  5. Step 5: Solve for x
    x = 265,225/399
  6. Step 6: Final answer
    x = 664.72

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Why These Related Problems?

These problems maintain the same ratio (1.29) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.