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Finding the Fourth Proportional to 121.86, 168.15 and 78.18

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Solution

The fourth proportional to 121.86, 168.15 and 78.18 is: 107.88

Step by Step Solution

  1. Step 1: Write the proportion equation
    121.86 : 168.15 = 78.18 : x
  2. Step 2: Convert to fraction form
    121.86/168.15 = 78.18/x
  3. Step 3: Cross multiply
    121.86x = 168.15 × 78.18
  4. Step 4: Simplify right side
    121.86x = 13,145.97
  5. Step 5: Solve for x
    x = 13,145.97/121.86
  6. Step 6: Final answer
    x = 107.88

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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.