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Finding the Fourth Proportional to 128.40, 177.20 and 78.56

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Solution

The fourth proportional to 128.40, 177.20 and 78.56 is: 108.42

Step by Step Solution

  1. Step 1: Write the proportion equation
    128.40 : 177.20 = 78.56 : x
  2. Step 2: Convert to fraction form
    128.40/177.20 = 78.56/x
  3. Step 3: Cross multiply
    128.40x = 177.20 × 78.56
  4. Step 4: Simplify right side
    128.40x = 13,920.83
  5. Step 5: Solve for x
    x = 13,920.83/128.40
  6. Step 6: Final answer
    x = 108.42

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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.