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Finding the Fourth Proportional to 90.78, 135.39 and 87.12

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Solution

The fourth proportional to 90.78, 135.39 and 87.12 is: 129.93

Step by Step Solution

  1. Step 1: Write the proportion equation
    90.78 : 135.39 = 87.12 : x
  2. Step 2: Convert to fraction form
    90.78/135.39 = 87.12/x
  3. Step 3: Cross multiply
    90.78x = 135.39 × 87.12
  4. Step 4: Simplify right side
    90.78x = 11,795.18
  5. Step 5: Solve for x
    x = 11,795.18/90.78
  6. Step 6: Final answer
    x = 129.93

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Why These Related Problems?

These problems maintain the same ratio (1.49) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.