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Finding the Fourth Proportional to 78.20, 117.29 and 20.42

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Solution

The fourth proportional to 78.20, 117.29 and 20.42 is: 30.62

Step by Step Solution

  1. Step 1: Write the proportion equation
    78.20 : 117.29 = 20.42 : x
  2. Step 2: Convert to fraction form
    78.20/117.29 = 20.42/x
  3. Step 3: Cross multiply
    78.20x = 117.29 × 20.42
  4. Step 4: Simplify right side
    78.20x = 2,394.37
  5. Step 5: Solve for x
    x = 2,394.37/78.20
  6. Step 6: Final answer
    x = 30.62

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Why These Related Problems?

These problems maintain the same ratio (1.50) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.