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Finding the Fourth Proportional to 85.75, 128.45 and 72

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Solution

The fourth proportional to 85.75, 128.45 and 72 is: 107.85

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.75 : 128.45 = 72 : x
  2. Step 2: Convert to fraction form
    85.75/128.45 = 72/x
  3. Step 3: Cross multiply
    85.75x = 128.45 × 72
  4. Step 4: Simplify right side
    85.75x = 9,248.40
  5. Step 5: Solve for x
    x = 9,248.40/85.75
  6. Step 6: Final answer
    x = 107.85

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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.