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Finding the Fourth Proportional to 87.99, 121.42 and 78.20

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Solution

The fourth proportional to 87.99, 121.42 and 78.20 is: 107.90

Step by Step Solution

  1. Step 1: Write the proportion equation
    87.99 : 121.42 = 78.20 : x
  2. Step 2: Convert to fraction form
    87.99/121.42 = 78.20/x
  3. Step 3: Cross multiply
    87.99x = 121.42 × 78.20
  4. Step 4: Simplify right side
    87.99x = 9,494.55
  5. Step 5: Solve for x
    x = 9,494.55/87.99
  6. Step 6: Final answer
    x = 107.90

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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.