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Finding the Fourth Proportional to 128.49, 177.20 and 81.79

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Solution

The fourth proportional to 128.49, 177.20 and 81.79 is: 112.80

Step by Step Solution

  1. Step 1: Write the proportion equation
    128.49 : 177.20 = 81.79 : x
  2. Step 2: Convert to fraction form
    128.49/177.20 = 81.79/x
  3. Step 3: Cross multiply
    128.49x = 177.20 × 81.79
  4. Step 4: Simplify right side
    128.49x = 14,493.19
  5. Step 5: Solve for x
    x = 14,493.19/128.49
  6. Step 6: Final answer
    x = 112.80

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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.