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Finding the Fourth Proportional to 128.96, 178.20 and 121.76

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Solution

The fourth proportional to 128.96, 178.20 and 121.76 is: 168.25

Step by Step Solution

  1. Step 1: Write the proportion equation
    128.96 : 178.20 = 121.76 : x
  2. Step 2: Convert to fraction form
    128.96/178.20 = 121.76/x
  3. Step 3: Cross multiply
    128.96x = 178.20 × 121.76
  4. Step 4: Simplify right side
    128.96x = 21,697.63
  5. Step 5: Solve for x
    x = 21,697.63/128.96
  6. Step 6: Final answer
    x = 168.25

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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.