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Finding the Third Proportional to 390 and 678

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Solution

The third proportional to 390 and 678 is: 1,178.68

Step by Step Solution

  1. Step 1: Write the proportion equation
    390 : 678 = 678 : x
  2. Step 2: Convert to fraction form
    390/678 = 678/x
  3. Step 3: Cross multiply
    390x = 678 × 678
  4. Step 4: Simplify right side
    390x = 459,684
  5. Step 5: Solve for x
    x = 459,684/390
  6. Step 6: Final answer
    x = 1,178.68

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Why These Related Problems?

These problems maintain the same ratio (1.74) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.