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Finding the Fourth Proportional to 708.90, 978.28 and 398.40

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Solution

The fourth proportional to 708.90, 978.28 and 398.40 is: 549.79

Step by Step Solution

  1. Step 1: Write the proportion equation
    708.90 : 978.28 = 398.40 : x
  2. Step 2: Convert to fraction form
    708.90/978.28 = 398.40/x
  3. Step 3: Cross multiply
    708.90x = 978.28 × 398.40
  4. Step 4: Simplify right side
    708.90x = 389,746.75
  5. Step 5: Solve for x
    x = 389,746.75/708.90
  6. Step 6: Final answer
    x = 549.79

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Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.