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Finding the Third Proportional to 639 and 1,380

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Solution

The third proportional to 639 and 1,380 is: 2,980.28

Step by Step Solution

  1. Step 1: Write the proportion equation
    639 : 1,380 = 1,380 : x
  2. Step 2: Convert to fraction form
    639/1,380 = 1,380/x
  3. Step 3: Cross multiply
    639x = 1,380 × 1,380
  4. Step 4: Simplify right side
    639x = 1,904,400
  5. Step 5: Solve for x
    x = 1,904,400/639
  6. Step 6: Final answer
    x = 2,980.28

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Why These Related Problems?

These problems maintain the same ratio (2.16) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.