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Finding the Fourth Proportional to 128.78, 177.73 and 78.98

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Solution

The fourth proportional to 128.78, 177.73 and 78.98 is: 109.01

Step by Step Solution

  1. Step 1: Write the proportion equation
    128.78 : 177.73 = 78.98 : x
  2. Step 2: Convert to fraction form
    128.78/177.73 = 78.98/x
  3. Step 3: Cross multiply
    128.78x = 177.73 × 78.98
  4. Step 4: Simplify right side
    128.78x = 14,037.36
  5. Step 5: Solve for x
    x = 14,037.36/128.78
  6. Step 6: Final answer
    x = 109.01

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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.