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Finding the Fourth Proportional to 100.80, 138.78 and 81.36

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Solution

The fourth proportional to 100.80, 138.78 and 81.36 is: 112.02

Step by Step Solution

  1. Step 1: Write the proportion equation
    100.80 : 138.78 = 81.36 : x
  2. Step 2: Convert to fraction form
    100.80/138.78 = 81.36/x
  3. Step 3: Cross multiply
    100.80x = 138.78 × 81.36
  4. Step 4: Simplify right side
    100.80x = 11,291.14
  5. Step 5: Solve for x
    x = 11,291.14/100.80
  6. Step 6: Final answer
    x = 112.02

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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.