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Finding the Fourth Proportional to 821.20, 1,230.30 and 387.40

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Solution

The fourth proportional to 821.20, 1,230.30 and 387.40 is: 580.39

Step by Step Solution

  1. Step 1: Write the proportion equation
    821.20 : 1,230.30 = 387.40 : x
  2. Step 2: Convert to fraction form
    821.20/1,230.30 = 387.40/x
  3. Step 3: Cross multiply
    821.20x = 1,230.30 × 387.40
  4. Step 4: Simplify right side
    821.20x = 476,618.22
  5. Step 5: Solve for x
    x = 476,618.22/821.20
  6. Step 6: Final answer
    x = 580.39

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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.