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Finding the Fourth Proportional to 121.89, 168.20 and 78.20

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Solution

The fourth proportional to 121.89, 168.20 and 78.20 is: 107.90

Step by Step Solution

  1. Step 1: Write the proportion equation
    121.89 : 168.20 = 78.20 : x
  2. Step 2: Convert to fraction form
    121.89/168.20 = 78.20/x
  3. Step 3: Cross multiply
    121.89x = 168.20 × 78.20
  4. Step 4: Simplify right side
    121.89x = 13,152.01
  5. Step 5: Solve for x
    x = 13,152.01/121.89
  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.