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Finding the Fourth Proportional to 87.20, 120.36 and 78.40

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Solution

The fourth proportional to 87.20, 120.36 and 78.40 is: 108.21

Step by Step Solution

  1. Step 1: Write the proportion equation
    87.20 : 120.36 = 78.40 : x
  2. Step 2: Convert to fraction form
    87.20/120.36 = 78.40/x
  3. Step 3: Cross multiply
    87.20x = 120.36 × 78.40
  4. Step 4: Simplify right side
    87.20x = 9,436.22
  5. Step 5: Solve for x
    x = 9,436.22/87.20
  6. Step 6: Final answer
    x = 108.21

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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.