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Finding the Fourth Proportional to 128.20, 176.80 and 86.20

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Solution

The fourth proportional to 128.20, 176.80 and 86.20 is: 118.88

Step by Step Solution

  1. Step 1: Write the proportion equation
    128.20 : 176.80 = 86.20 : x
  2. Step 2: Convert to fraction form
    128.20/176.80 = 86.20/x
  3. Step 3: Cross multiply
    128.20x = 176.80 × 86.20
  4. Step 4: Simplify right side
    128.20x = 15,239.73
  5. Step 5: Solve for x
    x = 15,239.73/128.20
  6. Step 6: Final answer
    x = 118.88

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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.