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Finding the Third Proportional to 390 and 644

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Solution

The third proportional to 390 and 644 is: 1,063.43

Step by Step Solution

  1. Step 1: Write the proportion equation
    390 : 644 = 644 : x
  2. Step 2: Convert to fraction form
    390/644 = 644/x
  3. Step 3: Cross multiply
    390x = 644 × 644
  4. Step 4: Simplify right side
    390x = 414,736
  5. Step 5: Solve for x
    x = 414,736/390
  6. Step 6: Final answer
    x = 1,063.43

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Why These Related Problems?

These problems maintain the same ratio (1.65) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.