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Finding the Third Proportional to 390.88 and 639.75

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Solution

The third proportional to 390.88 and 639.75 is: 1,047.09

Step by Step Solution

  1. Step 1: Write the proportion equation
    390.88 : 639.75 = 639.75 : x
  2. Step 2: Convert to fraction form
    390.88/639.75 = 639.75/x
  3. Step 3: Cross multiply
    390.88x = 639.75 × 639.75
  4. Step 4: Simplify right side
    390.88x = 409,280.06
  5. Step 5: Solve for x
    x = 409,280.06/390.88
  6. Step 6: Final answer
    x = 1,047.09

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Why These Related Problems?

These problems maintain the same ratio (1.64) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.