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Finding the Fourth Proportional to 98.78, 136.31 and 61.91

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Solution

The fourth proportional to 98.78, 136.31 and 61.91 is: 85.43

Step by Step Solution

  1. Step 1: Write the proportion equation
    98.78 : 136.31 = 61.91 : x
  2. Step 2: Convert to fraction form
    98.78/136.31 = 61.91/x
  3. Step 3: Cross multiply
    98.78x = 136.31 × 61.91
  4. Step 4: Simplify right side
    98.78x = 8,437.96
  5. Step 5: Solve for x
    x = 8,437.96/98.78
  6. Step 6: Final answer
    x = 85.43

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Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.