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Finding the Fourth Proportional to 128.72, 177.71 and 87.39

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Solution

The fourth proportional to 128.72, 177.71 and 87.39 is: 120.65

Step by Step Solution

  1. Step 1: Write the proportion equation
    128.72 : 177.71 = 87.39 : x
  2. Step 2: Convert to fraction form
    128.72/177.71 = 87.39/x
  3. Step 3: Cross multiply
    128.72x = 177.71 × 87.39
  4. Step 4: Simplify right side
    128.72x = 15,529.64
  5. Step 5: Solve for x
    x = 15,529.64/128.72
  6. Step 6: Final answer
    x = 120.65

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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.