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Finding the Fourth Proportional to 781.36, 1,171.56 and 390.90

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Solution

The fourth proportional to 781.36, 1,171.56 and 390.90 is: 586.12

Step by Step Solution

  1. Step 1: Write the proportion equation
    781.36 : 1,171.56 = 390.90 : x
  2. Step 2: Convert to fraction form
    781.36/1,171.56 = 390.90/x
  3. Step 3: Cross multiply
    781.36x = 1,171.56 × 390.90
  4. Step 4: Simplify right side
    781.36x = 457,968.66
  5. Step 5: Solve for x
    x = 457,968.66/781.36
  6. Step 6: Final answer
    x = 586.12

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Why These Related Problems?

These problems maintain the same ratio (1.50) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.