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Finding the Fourth Proportional to 87.78, 121.31 and 72.21

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Solution

The fourth proportional to 87.78, 121.31 and 72.21 is: 99.79

Step by Step Solution

  1. Step 1: Write the proportion equation
    87.78 : 121.31 = 72.21 : x
  2. Step 2: Convert to fraction form
    87.78/121.31 = 72.21/x
  3. Step 3: Cross multiply
    87.78x = 121.31 × 72.21
  4. Step 4: Simplify right side
    87.78x = 8,759.43
  5. Step 5: Solve for x
    x = 8,759.43/87.78
  6. Step 6: Final answer
    x = 99.79

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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.