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Finding the Fourth Proportional to 431.20, 646.80 and 138.70

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Solution

The fourth proportional to 431.20, 646.80 and 138.70 is: 208.05

Step by Step Solution

  1. Step 1: Write the proportion equation
    431.20 : 646.80 = 138.70 : x
  2. Step 2: Convert to fraction form
    431.20/646.80 = 138.70/x
  3. Step 3: Cross multiply
    431.20x = 646.80 × 138.70
  4. Step 4: Simplify right side
    431.20x = 89,711.16
  5. Step 5: Solve for x
    x = 89,711.16/431.20
  6. Step 6: Final answer
    x = 208.05

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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.