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Finding the Third Proportional to 390 and 669

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Solution

The third proportional to 390 and 669 is: 1,147.59

Step by Step Solution

  1. Step 1: Write the proportion equation
    390 : 669 = 669 : x
  2. Step 2: Convert to fraction form
    390/669 = 669/x
  3. Step 3: Cross multiply
    390x = 669 × 669
  4. Step 4: Simplify right side
    390x = 447,561
  5. Step 5: Solve for x
    x = 447,561/390
  6. Step 6: Final answer
    x = 1,147.59

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Why These Related Problems?

These problems maintain the same ratio (1.72) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.