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Finding the Fourth Proportional to 431.72, 647.42 and 139.21

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Solution

The fourth proportional to 431.72, 647.42 and 139.21 is: 208.76

Step by Step Solution

  1. Step 1: Write the proportion equation
    431.72 : 647.42 = 139.21 : x
  2. Step 2: Convert to fraction form
    431.72/647.42 = 139.21/x
  3. Step 3: Cross multiply
    431.72x = 647.42 × 139.21
  4. Step 4: Simplify right side
    431.72x = 90,127.34
  5. Step 5: Solve for x
    x = 90,127.34/431.72
  6. Step 6: Final answer
    x = 208.76

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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.