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Finding the Fourth Proportional to 85.70, 128.34 and 81.80

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Solution

The fourth proportional to 85.70, 128.34 and 81.80 is: 122.50

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.70 : 128.34 = 81.80 : x
  2. Step 2: Convert to fraction form
    85.70/128.34 = 81.80/x
  3. Step 3: Cross multiply
    85.70x = 128.34 × 81.80
  4. Step 4: Simplify right side
    85.70x = 10,498.21
  5. Step 5: Solve for x
    x = 10,498.21/85.70
  6. Step 6: Final answer
    x = 122.50

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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.