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Finding the Fourth Proportional to 280.78, 421.17 and 85.78

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Solution

The fourth proportional to 280.78, 421.17 and 85.78 is: 128.67

Step by Step Solution

  1. Step 1: Write the proportion equation
    280.78 : 421.17 = 85.78 : x
  2. Step 2: Convert to fraction form
    280.78/421.17 = 85.78/x
  3. Step 3: Cross multiply
    280.78x = 421.17 × 85.78
  4. Step 4: Simplify right side
    280.78x = 36,127.96
  5. Step 5: Solve for x
    x = 36,127.96/280.78
  6. Step 6: Final answer
    x = 128.67

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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.