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Finding the Fourth Proportional to 128.78, 177.79 and 91.47

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Solution

The fourth proportional to 128.78, 177.79 and 91.47 is: 126.28

Step by Step Solution

  1. Step 1: Write the proportion equation
    128.78 : 177.79 = 91.47 : x
  2. Step 2: Convert to fraction form
    128.78/177.79 = 91.47/x
  3. Step 3: Cross multiply
    128.78x = 177.79 × 91.47
  4. Step 4: Simplify right side
    128.78x = 16,263.06
  5. Step 5: Solve for x
    x = 16,263.06/128.78
  6. Step 6: Final answer
    x = 126.28

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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.