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Finding the Third Proportional to 390 and 489

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Solution

The third proportional to 390 and 489 is: 613.13

Step by Step Solution

  1. Step 1: Write the proportion equation
    390 : 489 = 489 : x
  2. Step 2: Convert to fraction form
    390/489 = 489/x
  3. Step 3: Cross multiply
    390x = 489 × 489
  4. Step 4: Simplify right side
    390x = 239,121
  5. Step 5: Solve for x
    x = 239,121/390
  6. Step 6: Final answer
    x = 613.13

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These problems maintain the same ratio (1.25) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.