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Finding the Fourth Proportional to 100.75, 138.90 and 78.88

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Solution

The fourth proportional to 100.75, 138.90 and 78.88 is: 108.75

Step by Step Solution

  1. Step 1: Write the proportion equation
    100.75 : 138.90 = 78.88 : x
  2. Step 2: Convert to fraction form
    100.75/138.90 = 78.88/x
  3. Step 3: Cross multiply
    100.75x = 138.90 × 78.88
  4. Step 4: Simplify right side
    100.75x = 10,956.43
  5. Step 5: Solve for x
    x = 10,956.43/100.75
  6. Step 6: Final answer
    x = 108.75

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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.