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Finding the Fourth Proportional to 81.19, 121.65 and 78.31

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Solution

The fourth proportional to 81.19, 121.65 and 78.31 is: 117.33

Step by Step Solution

  1. Step 1: Write the proportion equation
    81.19 : 121.65 = 78.31 : x
  2. Step 2: Convert to fraction form
    81.19/121.65 = 78.31/x
  3. Step 3: Cross multiply
    81.19x = 121.65 × 78.31
  4. Step 4: Simplify right side
    81.19x = 9,526.41
  5. Step 5: Solve for x
    x = 9,526.41/81.19
  6. Step 6: Final answer
    x = 117.33

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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.