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Finding the Fourth Proportional to 85.90, 128.92 and 42.58

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Solution

The fourth proportional to 85.90, 128.92 and 42.58 is: 63.90

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.90 : 128.92 = 42.58 : x
  2. Step 2: Convert to fraction form
    85.90/128.92 = 42.58/x
  3. Step 3: Cross multiply
    85.90x = 128.92 × 42.58
  4. Step 4: Simplify right side
    85.90x = 5,489.41
  5. Step 5: Solve for x
    x = 5,489.41/85.90
  6. Step 6: Final answer
    x = 63.90

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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.