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Finding the Fourth Proportional to 128.70, 177.54 and 87.21

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Solution

The fourth proportional to 128.70, 177.54 and 87.21 is: 120.31

Step by Step Solution

  1. Step 1: Write the proportion equation
    128.70 : 177.54 = 87.21 : x
  2. Step 2: Convert to fraction form
    128.70/177.54 = 87.21/x
  3. Step 3: Cross multiply
    128.70x = 177.54 × 87.21
  4. Step 4: Simplify right side
    128.70x = 15,483.26
  5. Step 5: Solve for x
    x = 15,483.26/128.70
  6. Step 6: Final answer
    x = 120.31

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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.