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Finding the Fourth Proportional to 421.20, 631.78 and 128.70

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Solution

The fourth proportional to 421.20, 631.78 and 128.70 is: 193.04

Step by Step Solution

  1. Step 1: Write the proportion equation
    421.20 : 631.78 = 128.70 : x
  2. Step 2: Convert to fraction form
    421.20/631.78 = 128.70/x
  3. Step 3: Cross multiply
    421.20x = 631.78 × 128.70
  4. Step 4: Simplify right side
    421.20x = 81,309.76
  5. Step 5: Solve for x
    x = 81,309.76/421.20
  6. Step 6: Final answer
    x = 193.04

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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.